Added code coverage

Author: maitraysuthar

.travis.yml

@@ -3,6 +3,18 @@ node_js:
   - '12'
   - '10'
   - '8'
+branches:
+  only:
+    - master
+cache:
+  npm: true
+services:
+  - mongodb
+before_script:
+  - cp .env.example .env
+env:
+  - NODE_ENV=test
+  - MONGODB_URL=mongodb://127.0.0.1:27017/rest-api-nodejs-mongodb
 os:
   - windows
   - linux