chore(testing): add integration with codecov

Author: ultrox

.travis.yml

@@ -8,10 +8,12 @@ notifications:
 node_js:
   - '10'
   - '11'
-install: npm install
+install:
+  - npm install -g semantic-release codecov
+  - npm install
 script: npm t
 after_success:
-  - npm install -g semantic-release
   - semantic-release
+  - codecov
 branches:
   only: master