Skip parentheses on singleton class declaration

[soutaro]

Parsing Ruby code with singleton class declaration with assignment generates a class name with (.

This is the example of the source code.

module DidYouMean
  class << (NameErrorCheckers = Object.new)
  end
end

This generates DidYouMean::(NameErrorCheckers class, and raises an error during load.

.../rdoc/lib/rdoc/store.rb:530:in `block in load_all': end pattern with unmatched parenthesis: /^DidYouMean::(NameErrorCheckers::[^:]+$/ (RegexpError)

This PR fixes the issue by ignoring surrounding parentheses.

[soutaro]

I found the problem with the rbs annotate command which calls RDoc::Store#load_all. ri shows a problem related to this with the following output:

$ make rdoc RDOCFLAGS="--visibility=nodoc"
$ ri --no-system -d .ext/rdoc DidYouMean::NameErrorCheckers
Nothing known about DidYouMean::NameErrorCheckers
Did you mean?  DidYouMean::(NameErrorCheckers
               DidYouMean::KeyErrorChecker