Add Circle CI config and remove Travis CI config (open-telemetry#233)

Also update Makefile to build tools locally.
Similar to open-telemetry/oteps#14.

.circleci/config.yml

@@ -0,0 +1,12 @@
+
+version: 2
+
+jobs:
+  build:
+    docker:
+      - image: circleci/golang:1.12
+    steps:
+      - checkout
+      - run:
+          name: Verify
+          command: make precommit

.gitignore

@@ -20,4 +20,7 @@ bin
 \#*\#
 
 # Vim
-.swp
+.swp
+
+# Misspell binary
+.tools

CONTRIBUTING.md

@@ -26,7 +26,7 @@ To check for typos, use
 
 ```bash
 # Golang is needed for the misspell tool.
-make install-tools
+make install-misspell
 make misspell
 ```
 

Makefile

@@ -1,21 +1,20 @@
 # All documents to be used in spell check.
 ALL_DOC := $(shell find . -name '*.md' -type f | sort)
 
-MISSPELL=misspell -error
-MISSPELL_CORRECTION=misspell -w
+TOOLS_DIR := ./.tools
+MISSPELL_BINARY=$(TOOLS_DIR)/misspell
 
-.PHONY: travis-ci
-travis-ci: misspell
+.PHONY: precommit
+precommit: install-misspell misspell
 
-.PHONY: misspell
+ .PHONY: install-misspell
+install-misspell: go.mod go.sum internal/tools.go
+	go build -o $(MISSPELL_BINARY) github.com/client9/misspell/cmd/misspell
+
+ .PHONY: misspell
 misspell:
-	$(MISSPELL) $(ALL_DOC)
+	$(MISSPELL_BINARY) -error $(ALL_DOCS)
 
-.PHONY: misspell-correction
+ .PHONY: misspell-correction
 misspell-correction:
-	$(MISSPELL_CORRECTION) $(ALL_DOC)
-
-.PHONY: install-tools
-install-tools:
-	GO111MODULE=on go install \
-	  github.com/client9/misspell/cmd/misspell
+	$(MISSPELL_BINARY) -w $(ALL_DOCS)