Fix lib/rack-patch.rb for MRI 2.2.0 and Rbx 2.3.0 on Ubuntu

[jodosha]

Closes #59

[runlevel5]

I manually test the sort_by in Ruby 2.1 and 2.2 yet I could not reproduce the bug. I think there is something in the Rack implementation or somewhere might monkey-patch or do something that cause side-effect on sort_by

[coveralls]

Changes Unknown when pulling 15f7594 on fix-rack-utils-mri-2-2-0 into * on master*.

[jodosha]

@JONESLEE85 Which OS? Have you tried with the array_sort_by.rb test reported in #59? That's just plain Ruby without gems.

[runlevel5]

@jodosha I tried it on my OSX.

[jodosha]

@JONESLEE85 Yeah, it works on OS X 10.9 (my machine), but not on Ubuntu.

[runlevel5]

@jodosha my point is that the results of array_sort_by.rb are the same :| - it should be different right?

[jodosha]

@JONESLEE85 they should be the same across all the Ruby versions and OS.
OS X has consistent results across Ruby 2.0 to 2.2.
Ubuntu has inconsistent results with 2.2. From 2.0 to 2.1 it works like OS X.

[runlevel5]

@jodosha that's right, it is only Linux-related. Have you lodged an error with Rack?