Discussion note icon shows up when you click on diff on touch screen

Fixes #15104 

* Fix bug that stopped discussion note button from showing up on iOS
* Shifted button a few `px` to fix slight cutoff
<div>
<img src="/uploads/9d507091f33aa69ef68323386bf3a5c2/Screen_Shot_2016-04-15_at_12.08.46_PM.png" width="300px">
<img src="/uploads/a964a2a46636cbe4593abf272b5796f7/Screen_Shot_2016-04-15_at_12.11.40_PM.png" width="300px">
</div>

See merge request !3755