Relax the RE for Blender download

- add a lazy wildcard after the OS X version number but before
  the %ARCH% substitution. This lets us match what the current
  URLs show (from the first mirror listed here):
  http://ftp.nluug.nl/pub/graphics/blender/release/Blender2.71/blender-2.71-OSX_10.6-j2k-fix-x86_64.zip
Merge pull request #5 from timsutton/blender-url-relax

Relax the RE for Blender download