Fix apple/nvidia shader compilation issue.
Fix apple/nvidia shader compilation issue.

2 -> 2.0 so that the compiler knows it's a float.


git-svn-id: 83c4c97093aeea62ac982fbfd516bf9db27f5c99@1679 c36c8488-0289-0348-9b64-b301f74bd9a7

BlueBrain/Tuvok,BlueBrain/Tuvok,BlueBrain/Tuvok