Update indexOf polyfill

Updated from the same source as the original comment. If IE8 isn’t
supported then this can be removed.
Add JSHint to Travis validation

Run before the install as it acts as a fast fail vs the gem install time
Add jshintignore for failing files
JSHint: Add strict comparisons to poll_ui.js
Merge pull request #2092 from nschonni/jshinting

Jshinting during CI build