Restrict `radix` usage to its base module so that it doesn't affect
Ruby's `String.b`.

Spider-Gazelle's usage of radix doesn't need the whole gem required
and the current approach is an issue with at least [MRI's
ERB](https://github.com/ruby/ruby/blob/trunk/lib/erb.rb#L600).
Merge pull request #1 from dariocravero/restrict-radix

Restrict `radix` usage to its base module so that it doesn't affect Ruby's `String.b`