Update travis to build and test

Author: styfle

.travis.yml

@@ -1,6 +1,8 @@
 language: node_js
 
 node_js:
-  - "4"
-  - "6"
   - "8"
+
+script:
+  - npm run build
+  - npm run test

README.md

@@ -1,6 +1,7 @@
 # react-server-example-tsx
 
 [![npm](https://img.shields.io/npm/v/react-server-example-tsx.svg?maxAge=2592000)](https://www.npmjs.com/package/react-server-example-tsx)
+[![Downloads](https://img.shields.io/npm/dt/react-server-example-tsx.svg)](https://www.npmjs.com/package/react-server-example-tsx)
 [![Dependency Status](https://david-dm.org/styfle/react-server-example-tsx.svg)](https://david-dm.org/styfle/react-server-example-tsx)
 [![devDependency Status](https://david-dm.org/styfle/react-server-example-tsx/dev-status.svg)](https://david-dm.org/styfle/react-server-example-tsx#info=devDependencies)