When create a pre-compiled gem in MinGW MSYS shell passing Ruby or OpenCV's paths,
the paths are converted to be invalid by MSYS shell.
E.g.
When we run the following command
$ rake gem:precompile RUBIES=C:/ruby19/bin/ruby.exe,C:/ruby20/bin/ruby.exe
The following paths are expected
ENV['RUBIES'] = "C:/ruby19/bin/ruby.exe,C:/ruby20/bin/ruby.exe"
But we get the following
ENV['RUBIES'] = "C;C:\\MinGW\\msys\\1.0\\ruby19\\bin\\ruby.exe,C;C:\\MinGW\\msys\\1.0\\ruby20\\bin\\ruby.exe"
This fix is for avoiding the problem.
