Bump RDoc version to 6.16.1 (ruby#15344)

Author: st0012

gems/bundled_gems

@@ -39,7 +39,7 @@ ostruct             0.6.3   https://github.com/ruby/ostruct
 pstore              0.2.0   https://github.com/ruby/pstore
 benchmark           0.5.0   https://github.com/ruby/benchmark
 logger              1.7.0   https://github.com/ruby/logger
-rdoc                6.16.0  https://github.com/ruby/rdoc
+rdoc                6.16.1  https://github.com/ruby/rdoc
 win32ole            1.9.2   https://github.com/ruby/win32ole
 irb                 1.15.3  https://github.com/ruby/irb
 reline              0.6.3   https://github.com/ruby/reline