Update .travis.yml

.travis.yml

@@ -1,9 +1,6 @@
 language: node_js
 node_js:
-  - '12'
+  - 'stable'
-before_install:
+install: npm install
-  # Update the npm client. Older clients cannot, e.g., handle scoped modules.
+script: npm start
-  - npm update -g npm
+after_success: npm run coverage
-after_script:
-  - npm run coverage
-  - npm start