Does not display tripple-backticks-language correctly

[grosser]

http://github-preview.herokuapp.com/?text=%23+Installation%0A%0A++++gem+install+bump%0A%0A%23+Usage%0A%0ACurrent+version+of+your+gem%3A%0A%0A++++bump+current%0A%0ACurrent+version%3A+0.1.2%0A%0ABump+your+gemfile+%28major%2C+minor%2C+patch%29%3A%0A%0A++++bump+patch%0A%0ABump+version+0.1.2+to+0.1.3%0A%0A%23%23%23+Rake%0A%0A%60%60%60Ruby%0A%23+Rakefile%0Arequire+%22bump%2Ftasks%22%0A%60%60%60%0A%0A++++rake+bump%3Apatch%0A++++rake+bump%3Acurrent%0A%0A%23+Supported+locations%0A+-+VERSION+file+with+%221.2.3%22%0A+-+gemspec+with+%60gem.version+%3D+%221.2.3%22%60%0A+-+lib%2F%2A%2A%2Fversion.rb+file+with+%60VERSION+%3D+%221.2.3%22%60%0A%0A%23+Todo%0A%0A+-+Handle+options+properly%0A+-+%60VERSION+%3D+%221.2.3%22%60+in+lib%2F%2A.rb%0A+-+gemspec+with+%60Gem%3A%3ASpecification.new+%22gem-name%22%2C+%221.2.3%22+do%60%0A%0A%23+Author%0AGregory%3Cbr%2F%3E%0ALicense%3A+MIT%3Cbr%2F%3E%0A%5B%21%5BBuild+Status%5D%28https%3A%2F%2Ftravis-ci.org%2Fgregorym%2Fbump.png%29%5D%28https%3A%2F%2Ftravis-ci.org%2Fgregorym%2Fbump%29%0A%0A%0A

vs

https://github.com/grosser/bump/tree/rake

[kei-s]

I think, it is because github-markup gem (https://github.com/github/markup) is not support syntax highlighting.
There are some pull-reqs(e.g. github/markup#39), not merged yet.