fix: allow usage as formatter (#129)

Author: ms-jpq

lib/syntax_tree/rbs.rb

@@ -41,7 +41,7 @@ def force_parens?
     end
 
     class << self
-      def format(source, maxwidth = 80)
+      def format(source, maxwidth = 80, _options = {})
         formatter = Formatter.new(source, [], maxwidth)
         parse(source).format(formatter)