pipeline: test full build in travis to detect feature issues with cra (#85)

Author: byCedric

.travis.yml

@@ -12,6 +12,7 @@ script:
   - npx stylelint './src/**/*.js'
   - npx eslint ./src
   - npx react-scripts test --coverage
+  - npm run build
   - npm audit
 after_success:
   - npx codecov