Update to work with node 8 (#4)

Summary:
After running 'npm install', npm reported the follow warning message:

    npm WARN react-apollo@0.10.1 requires a peer of redux@^2.0.0 || ^3.0.0 but none was installed.

After running 'npm install redux --save-dev' the tests pass although there were
some errors logged to the console.

I've updated .travis.yml to use node 8 when running the tests.

Test Plan:
- npm test
- see that the tests pass on travis

Reviewers: csilvers

.travis.yml

@@ -1,3 +1,3 @@
 language: node_js
 node_js:
-    - "4.2"
+    - "8"