Fix syntax highlighting of sample bash and bibtex in rst markup.

[anntzer]

PR Summary

Current
https://matplotlib.org/devdocs/citing.html#citing-matplotlib
https://matplotlib.org/devdocs/faq/osx_framework.html#short-version

After PR:
https://1543-7439715-gh.circle-artifacts.com/0/home/circleci/project/doc/build/html/citing.html#citing-matplotlib
https://1543-7439715-gh.circle-artifacts.com/0/home/circleci/project/doc/build/html/faq/osx_framework.html#short-version

See sphinx-doc/sphinx#2155 for (likely) why .. code:: foo is not working.

PR Checklist

• Has Pytest style unit tests
• Code is PEP 8 compliant
• New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way