bundler trait infinite loop on windows

[dub357]

If warbler cannot find the bundler.gemspec (a problem when bundler is installed as a 'default' gem via rubygems and likely a separate issue), then the search through the parent directory tree results in an infinite loop on Windows because the check (which uses a regular expression) only ends the loop if the path is either "." or "/". Neither of these represents the root path on Windows.

https://github.com/jruby/warbler/blob/5ce7ec0dbe6c0f43d671c3f4a88f110838791b1c/lib/warbler/traits/bundler.rb#L48