Update rbs

gems/bundled_gems

@@ -5,5 +5,5 @@ rake 13.0.1 https://github.com/ruby/rake
 test-unit 3.3.7 https://github.com/test-unit/test-unit 3.3.7
 rexml 3.2.4 https://github.com/ruby/rexml
 rss 0.2.9 https://github.com/ruby/rss 0.2.9
-rbs 0.19.0 https://github.com/ruby/rbs
+rbs 0.20.0 https://github.com/ruby/rbs
 typeprof 0.8.0 https://github.com/ruby/typeprof