Ignores the case of the dictionary keys.

Steam apparently doesnt care what case the dictionary keys in
shortcuts.vdf are. I got a vdf file which (Im assuming because of a
different version of Steam) used "appname", "exe", and "StartDir" for
their keys instead of "AppName", "Exe", and "StartDir". This commit
fixes the issue those vdf files cause by making the regular expression
case insensitive.