fix(travis): good bye yarn

Author: pine

.travis.yml

@@ -5,16 +5,8 @@ node_js:
   - 8
   - stable
 
-before_install:
-  - curl -o- -L https://yarnpkg.com/install.sh | bash -s -- --version 1.3.2
-  - export PATH=$HOME/.yarn/bin:$PATH
-install::
-  - travis_retry yarn
 test::
-  - travis_retry yarn test
-
-cache:
-    yarn: true
+  - travis_retry npm test
 
 env:
   global: