Add curl into the LIBS in the make file

I'm using Ubuntu 12.04 64-bit,  and I run into this error during the make process:
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/home/jason/github/uvbook/code/uvwget/main.c:50: undefined reference to `curl_easy_init'
/home/jason/github/uvbook/code/uvwget/main.c:51: undefined reference to `curl_easy_setopt'
/home/jason/github/uvbook/code/uvwget/main.c:52: undefined reference to `curl_easy_setopt'
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I added lcurl into the LIBS variable, the problem's gone.