Fix formatting consistency in app.js

Changed "/tab" at line 21 to '/tab' to keep quotation mark formatting consistent across app.js

![screen shot 2014-07-11 at 10 31 10 am](https://cloud.githubusercontent.com/assets/5373129/3556276/1d455eb0-0922-11e4-968f-ec841d1afe49.png)
![screen shot 2014-07-11 at 10 32 06 am](https://cloud.githubusercontent.com/assets/5373129/3556274/17696a40-0922-11e4-954b-6de428c15c2f.png)