Modify Makefile to work with ubuntu

```-lcurl -lm``` 兩個參數要放到最後面，在 ubuntu 才能正確編譯，參考：
* http://curl.haxx.se/mail/lib-2012-06/0275.html
* http://www.cnblogs.com/flyingchen/archive/2011/10/26/2225339.html