chore(ci): added codecov in the travis configuration

Author: AnthonyNahas

.travis.yml

@@ -17,10 +17,14 @@ before_script:
   - export DISPLAY=:99.0
   - sh -e /etc/init.d/xvfb start
   - npm install --quiet -g gulp-cli
+  - npm install codecov -g
 
 script: gulp test:ci
 
-after_success: gulp coveralls
+after_success:
+  - gulp coveralls
+  - codecov
 
 cache:
-  yarn: true
+  directories:
+  - node_modules # NPM packages