doc: update luarocks install instructions.
doc: update luarocks install instructions.

* README.md (Installation): Update to reference moonscript rocks
repository, which has better uptime than the default luarocks
domain used by released LuaRocks.

Signed-off-by: Gary V. Vaughan <f9023000f29773649f3850298becb9544b5fd6a9@gnu.org>

snegovick/luaposix,rrthomas/luaposix,ardje/luaposix,zevv/luaposix,jimmyharris/luaposix,rrthomas/luaposix,snegovick/luaposix,luaposix/luaposix,jimmyharris/luaposix,ardje/luaposix,zevv/luaposix