Define Ripper::Lexer::Elem#to_s

Alias `#inspect` as `#to_s` also in the new `Ripper::Lexer::Elem`
class, so that `puts Ripper::Lexer.new(code).scan` shows the
attributes.

ext/ripper/lib/ripper/lexer.rb

@@ -119,6 +119,8 @@ class Ripper
         "#<#{self.class}: #{event}@#{pos[0]}:#{pos[1]}:#{state}: #{tok.inspect}#{": " if message}#{message}>"
       end
 
+      alias to_s inspect
+
       def pretty_print(q)
         q.group(2, "#<#{self.class}:", ">") {
           q.breakable