improve lua and luajit

packages/l/lua/xmake.lua

@@ -10,9 +10,7 @@ package("lua")
     add_versions("5.2.4", "b9e2e4aad6789b3b63a056d442f7b39f0ecfca3ae0f1fc0ae4e9614401b69f4b")
     add_versions("5.1.5", "2640fc56a795f29d28ef15e13c34a47e223960b0240e8cb0a82d9b0738695333")
 
-    on_load(function (package)
-        package:addvar("includedirs", "include/lua")
-    end)
+    add_includedirs("include/lua")
 
     on_install(function (package)
         io.writefile("xmake.lua", [[

packages/l/luajit/xmake.lua

@@ -14,9 +14,7 @@ package("luajit")
     add_versions("2.0.4", "620fa4eb12375021bef6e4f237cbd2dd5d49e56beb414bee052c746beef1807d")
     add_versions("2.0.5", "874b1f8297c697821f561f9b73b57ffd419ed8f4278c82e05b48806d30c1e979")
 
-    on_load(function (package)
-        package:addvar("includedirs", "include/luajit")
-    end)
+    add_includedirs("include/luajit")
 
     on_install("windows", function (package)
         os.cd("src")