Make def_*_delegator return name of method defined (Fixes #10)

[jeremyevans]

This restores compatibility with previous versions. This behavior
was previously undefined, but it makes sense for the name of the
defined method to be returned.

[ashmaroli]

Upon further thought to this, I think it'd be better to use a guard clause instead of initializing a local variable.

  def def_instance_delegator(accessor, method, ali = method)
    gen = Forwardable._delegator_method(self, accessor, method, ali)

    # If it's not a class or module, it's an instance
    mod = Module === self ? self : singleton_class

    unless RUBY_VERSION >= '2.7'
      return mod.module_eval(&gen)
    end

    mod.send(:ruby2_keywords, ali)
  end

[jeremyevans]

@ashmaroli I don't think that will work on Ruby 2.7+.

[ashmaroli]

I see.. Good to know that.
Thanks.