[chore] remove useless script in .travis.yml

Author: jin5354

.travis.yml

@@ -3,8 +3,6 @@ language: node_js
 env: PHANTOMJS_BIN=./node_modules/.bin/phantomjs
 node_js: 7
 script:
-  - rm -rf node_modules
-  - yarn
   - npm run lint
   - npm run test
   - npm run build