Replace checkint with checkinteger

one is an alias of the other, but one was removed in 5.3+, so it's
better to use the common function across all versions.

Author: mattsta

lua_cmsgpack.c

@@ -843,7 +843,7 @@ static int mp_unpack_one(lua_State *L) {
 }
 
 static int mp_unpack_limit(lua_State *L) {
-    int limit = luaL_checkint(L, 2);
+    int limit = luaL_checkinteger(L, 2);
     int offset = luaL_optint(L, 3, 0);
     /* Variable pop because offset may not exist */
     lua_pop(L, lua_gettop(L)-1);