Fix pygment lexer 500 errors when an alias is used instead of a name.
Created by: dosire
Fixes the following errors: https://github.com/gitlabhq/gitlabhq/issues/4074 https://github.com/gitlabhq/gitlabhq/issues/3257 https://github.com/gitlabhq/gitlabhq/issues/4015
and problem on GitLab Cloud