Normalize names in a URL

PyPI and Bandersnatch now normalize the project name in their URLs. This change matches that and will reduce the number of redirects we hit on PyPI and will reduce the need to hit /simple/ on a Bandersnatch mirror.

Note: This should not be merged until https://bitbucket.org/pypa/bandersnatch/pull-request/7/prefer-normalized-directory-names-but-keep/ is merged and released.