Fixes issue with signin button overflowing on mobile

Closes #14477

![Screen_Shot_2016-03-22_at_13.52.51](/uploads/7c9b2c38be7d497c690a7d17ae0ca76d/Screen_Shot_2016-03-22_at_13.52.51.png)

![Screen_Shot_2016-03-22_at_13.52.43](/uploads/8b2432aeb4afec455286fced11c5490c/Screen_Shot_2016-03-22_at_13.52.43.png)

See merge request !3342