Fix URI

> concerto_cas_auth at /usr/share/concerto/vendor/bundle/ruby/1.9.1/bundler/gems/concerto_cas_auth-0e63efb07e11 did not have a valid gemspec.
> This prevents bundler from installing bins or native extensions, but that may not affect its functionality.
> The validation message from Rubygems was:
>   "concerto-signage.org" is not a URI