rework travis file to use node_js and dl rust stable

.travis.yml

@@ -1,25 +1,22 @@
-language: rust
-rust:
-  - stable
-  - nightly
-os:
-  - linux
-  - osx
-  - windows
+language: node_js
+node_js:
+  - 12.0
 env:
   - NODE_ENV=ci
   - NODE_ENV=ci-staging
 cache: yarn
-
+os:
+  - linux
+  - osx
+  - windows
 before_install:
+  - curl https://sh.rustup.rs -sSf -m 60 | sh -s -- -y -v --default-toolchain stable
+  - if [[ "$TRAVIS_OS_NAME" == "windows" ]]; then HOME="/c/Users/travis"; fi
+  - export PATH="$HOME/.cargo/bin:$PATH"
   - rustup target add wasm32-unknown-unknown
-  - nvm install 12
-  - nvm use 12
   - npm install -g yarn
-
 install:
   - yarn install
-
 script:
   - yarn test
-  - yarn lint
+  - yarn lint