The last version of luarocks in tree is luarocks-2.0.12 (19 May 2013). Since then several versions have been released. The latest one is luarocks-2.1.2 (10 Jan 2014) Simply renaming the ebuild luarocks-2.0.12.ebuild to luarocks-2.1.2.ebuild works fine for me
The latest upstream version of luarocks is now 2.2.0: http://luarocks.org/en/Release_history
I confirm that renaming the ebuild also works for version 2.2.0.
+*luarocks-2.2.0 (21 Dec 2014) + + 21 Dec 2014; Rafael G. Martins <rafaelmartins@gentoo.org> + +luarocks-2.2.0.ebuild: + version bump. bug #500702 + thanks