Fix right arrow size for crate filter
This bug only appears when a crate has a long name:
<img width="1440" alt="screenshot 2018-12-08 at 16 36 21" src="https://user-images.githubusercontent.com/
3050060/
49687728-
7de06180-fb07-11e8-8554-
d32597351fac.png">
With this fix, it goes back to normal, whatever the size:
<img width="1440" alt="screenshot 2018-12-08 at 16 36 05" src="https://user-images.githubusercontent.com/
3050060/
49687730-
8769c980-fb07-11e8-91b7-
b5e1961211a2.png">
r? @QuietMisdreavus