enable MacOS.release in paraview-nightly

Casks/paraview-nightly.rb

@@ -2,7 +2,7 @@ cask :v1 => 'paraview-nightly' do
   version :latest
   sha256 :no_check
 
-  if MacOS.version < :mavericks
+  if MacOS.release < :mavericks
     url 'http://www.paraview.org/paraview-downloads/download.php?submit=Download&version=nightly&type=binary&os=osx&downloadFile=ParaView-Darwin-64bit-Lion-Python27-NIGHTLY.dmg'
   else
     url 'http://www.paraview.org/paraview-downloads/download.php?submit=Download&version=nightly&type=binary&os=osx&downloadFile=ParaView-Darwin-64bit-NIGHTLY.dmg'