Fix and improve js tests

This PR updates deploy filter according to https://github.com/zendesk/samson/pull/34/files
and intends to fix https://github.com/zendesk/samson/issues/36

I'm not familiar with Travis CI configuration, so I have no idea why the build passes when the js tests fail.
Could you take a look? @jwswj 

/cc @zendesk/samson 

### RISKS
- N/A