Add support for -moz-osx vendor prefix

Since Firefox 25 the vendor prefix `-moz-osx` is supported:
https://bugzilla.mozilla.org/show_bug.cgi?id=857142#c83

Add support for this vendor prefix to the `PropertySortOrder` linter.

Change-Id: Ib5b328bad6d2403dfe5fdf05debf188f0225282b
Reviewed-on: http://gerrit.causes.com/36110
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>