Rollup merge of #43795 - GuillaumeGomez:improve-variants-doc-style, r=QuietMisdreavus

Improve enum variants display

r? @rust-lang/docs

Before:

<img width="1440" alt="screen shot 2017-08-11 at 00 22 54" src="https://user-images.githubusercontent.com/3050060/29194776-728ce0e2-7e2b-11e7-8299-8300cc0c168b.png">

After:

<img width="1440" alt="screen shot 2017-08-11 at 00 22 57" src="https://user-images.githubusercontent.com/3050060/29194783-78867558-7e2b-11e7-9226-1327fd20163a.png">

(The doc of the variant is more aligned with the "[-]" now).

diff --cc src/librustdoc/html/static/rustdoc.css
Simple merge