Use msys2(32bit) instead of old msys

I've changed to use msys2 for ruby build so that parallel make works without hang.
Old msys has a bug of  parallel make.

Parallel make hangs due to msys bug.
http://sourceforge.net/p/mingw/bugs/1950/

msys2 is updated version of msys and the bug seems to be fixed.
http://mingw-users.1079350.n2.nabble.com/Status-of-MSYS2-td7582391.html