Migrating travis -> circle (snorkel-team#1685)

## Description of proposed changes
Replacing the CI system from Travis to Circle as we have seen issues running on Travis
## Related issue(s)
N/A
Fixes # (issue)
N/A
## Test plan
Having the CI tests run be Circle instead of Travis should test this 
## Checklist

Need help on these? Just ask!

* [x] I have read the **CONTRIBUTING** document.
* [x] I have updated the documentation accordingly.
* [x] I have added tests to cover my changes.
* [x] I have run `tox -e complex` and/or `tox -e spark` if appropriate.
* [x] All new and existing tests passed.

.circleci/config.yml

@@ -0,0 +1,154 @@
+# Use the latest 2.1 version of CircleCI pipeline process engine.
+version: 2.1
+
+orbs:
+  python: circleci/python@1.2
+
+commands:
+  setup_dependencies:
+    description: "Install depenencies"
+    parameters:
+      after-deps:
+        description: "Install dependenceis"
+        type: steps
+        default: []
+    steps:
+      - run: 
+          name: "Install open JDK"
+          command: sudo add-apt-repository -y ppa:openjdk-r/ppa
+      - run: 
+          name: "Install qq"
+          command: sudo apt-get -qq update
+      - run: 
+          name: "No install recommends for JDK"
+          command: sudo apt-get install -y openjdk-8-jdk --no-install-recommends
+      - run: 
+          name: "Run Java Alternatives install for JDK"
+          command: sudo update-java-alternatives -s java-1.8.0-openjdk-amd64
+      - run:
+          name: "Run pip install setup tools and wheel"
+          command: pip install -U pip setuptools wheel
+      - run:  
+          name: "Install Tox"
+          command: pip install -U tox==3.12.0
+      - run: 
+          name: "Install Code Cov"
+          command: pip install -U codecov
+      - steps: << parameters.after-deps >>
+
+# We want to make sure we run this only on master branch, release, or when we make tags
+run_complex: &run_complex
+  filters:
+    branches:
+      only:
+        - (master|release-v.*)
+    tags:
+      only: /.*/
+
+jobs:
+  Python38-Unit-Tests: 
+    docker:
+      - image: cimg/python:3.8
+    environment:
+      TOXENV: coverage,doctest,type,check 
+      TOX_INSTALL_DIR: .env
+      JAVA_HOME: /usr/lib/jvm/java-8-openjdk-amd64
+
+    steps:
+      - checkout
+      - setup_dependencies
+      - run:
+          name: "Run Tox"
+          command:  tox
+
+  Python37-Unit-Tests: 
+    docker:
+      - image: cimg/python:3.7
+    environment:
+      TOXENV: coverage,doctest,type,check 
+      TOX_INSTALL_DIR: .env
+      JAVA_HOME: /usr/lib/jvm/java-8-openjdk-amd64
+
+    steps:
+      - checkout
+      - setup_dependencies
+      - run:
+          name: "Run Tox"
+          command:  tox
+
+  Python36-Unit-Tests: 
+    docker:
+      - image: cimg/python:3.6
+    environment:
+      TOXENV: coverage,doctest,type,check 
+      TOX_INSTALL_DIR: .env
+      JAVA_HOME: /usr/lib/jvm/java-8-openjdk-amd64
+
+    steps:
+      - checkout
+      - setup_dependencies
+      - run:
+          name: "Run Tox"
+          command:  tox
+  Python38-Integration-Tests: 
+    docker:
+      - image: cimg/python:3.8
+    environment:
+      TOXENV: complex,type,check
+      TOX_INSTALL_DIR: .env
+      JAVA_HOME: /usr/lib/jvm/java-8-openjdk-amd64
+
+    steps:
+      - checkout
+      - setup_dependencies
+      - run:
+          name: "Run Tox"
+          command:  tox
+
+  Python37-Integration-Tests: 
+    docker:
+      - image: cimg/python:3.7
+    environment:
+      TOXENV: complex,spark,type,check
+      TOX_INSTALL_DIR: .env
+      JAVA_HOME: /usr/lib/jvm/java-8-openjdk-amd64
+
+    steps:
+      - checkout
+      - setup_dependencies
+      - run:
+          name: "Run Tox"
+          command:  tox
+
+  Python36-Integration-Tests: 
+    docker:
+      - image: cimg/python:3.6
+    environment:
+      TOXENV: coverage,complex,spark,doctest,type,check 
+      TOX_INSTALL_DIR: .env
+      JAVA_HOME: /usr/lib/jvm/java-8-openjdk-amd64
+
+    steps:
+      - checkout
+      - setup_dependencies
+      - run:
+          name: "Run Tox"
+          command:  tox
+
+workflows:
+  version: 2
+
+  Interation-Tests: 
+    jobs:
+      - Python38-Integration-Tests:
+          <<: *run_complex
+      - Python37-Integration-Tests:
+         <<: *run_complex
+      - Python36-Integration-Tests:
+          <<: *run_complex
+  Unit-Tests:
+    jobs:
+      - Python37-Unit-Tests
+      - Python36-Unit-Tests
+      - Python38-Unit-Tests
+

CONTRIBUTING.md

@@ -112,7 +112,7 @@ Any test that runs longer than half a second should be marked with the
 `@pytest.mark.complex` decorator.
 Typically, these will be integration tests or tests that verify complex
 properties like model convergence.
-We exclude long-running tests from the default `tox` and Travis builds
+We exclude long-running tests from the default `tox` and Circle CI builds
 on non-master and non-release branches to keep things moving fast.
 If you're touching areas of the code that could break a long-running test,
 you should include the results of `tox -e complex` in the PR's test plan.
@@ -124,7 +124,7 @@ To see the durations of the 10 longest-running tests, run
 
 PySpark tests are invoked separately from the rest since they require
 installing Java and the large PySpark package.
-They are executed on Travis, but not by default for a local `tox` command.
+They are executed on Circle CI, but not by default for a local `tox` command.
 If you're making changes to Spark-based operators, make sure you have
 Java 8 installed locally and then run `tox -e spark`.
 If you add a test that imports PySpark mark it with the