docs/css: remove hyphens in literals

[jrabbit]

Edited the sphinx css theme to prevent hyphens being inserted into the requirements.txt name and other literals.

right now:

with fix:

[GordonTheTurtle]

Please sign your commits following these rules:
https://github.com/moby/moby/blob/master/CONTRIBUTING.md#sign-your-work
The easiest way to do this is to amend the last commit:

$ git clone -b "patch-1" git@github.com:jrabbit/docker-py.git somewhere
$ cd somewhere
$ git commit --amend -s --no-edit
$ git push -f

Amending updates the existing PR. You DO NOT need to open a new one.

[milas]

Merged out-of-band to fix conflicts due to age. Thanks for the PR!