removed regexp version matching from mix.exs

When adding exlager as a dep in my mix project I got the following error:
** (Mix) Dependency specified in the wrong format: {:lager, %r".*", [git: "https://github.com/basho/lager.git"]}, expected { app :: atom, opts :: Keyword.t } | { app :: atom, requirement :: String.t
, opts :: Keyword.t }
Triggered by the depedency listing in the exlager project. Removed the regexp and it seems to work fine now.