luainstance: the name is "Lua", not "LUA"

Origin commit data
------------------
Commit: 4d7e07f81f
Author: Stefan Seyfried <seife@tuxbox-git.slipkontur.de>
Date: 2013-03-18 (Mon, 18 Mar 2013)

src/gui/plugins.cpp

@@ -354,7 +354,7 @@ void CPlugins::startLuaPlugin(int number)
 		       script, plugin_list[number].cfgfile.c_str());
 		return;
 	}
-	CLUAInstance *lua = new CLUAInstance();
+	CLuaInstance *lua = new CLuaInstance();
 	lua->runScript(script);
 	delete lua;
 }