Gemfile: remove pry-debugger because :mri_19
Gemfile: remove platforms from pry-byebug
Gemfile: remove :ruby_20 and :mingw_20 from syck
Gemfile: add :x64_mingw platform (aka RubyInstaller x64)

git-svn-id: http://svn.redmine.org/redmine/trunk@13651 e93f8b46-1217-0410-a6f0-8f06a7374b81