Build on freebsd

> Hi,
> 
> I got this email address from the commit log of node-stringprep-icu.
> 
> I'm wondering if you would be interested in accepted this attached diff which
makes the module build on FreeBSD, where ICU is installed in /usr/local by
default, which is not in the path.
> 
> Let me know if you like me to change anything.
> 
> Thanks in advance,
> 
> 
> --
> Ashish SHUKLA