Demo not working for users outside uberVU

Made it so when no labels are provided, the plugin will show all issues.

cc: @skidding @catalinmiron 
The reason I removed them was that if you initialized the plugin and set `githubLabels` to `[]` or `[bug]`(a single label) then the jQuery extend method would set it to `['bug', 'enhancement', 'feature']`. We can get around this by removing the deep extend [here](https://github.com/uberVU/github-changelog/blob/master/js/changelog.js#L32). What do you think?