Add missing library

[Farzat07]

Otherwise causes the following error on my machine:

/usr/bin/gem2arch:258:in `find_arch_version': uninitialized constant Net (NameError)

    resp = Net::HTTP.get_response(URI.parse(aur_request))
           ^^^
Did you mean?  Set
        from /usr/bin/gem2arch:427:in `block in check_gem_dependencies'
        from /usr/bin/gem2arch:424:in `each'
        from /usr/bin/gem2arch:424:in `check_gem_dependencies'
        from /usr/bin/gem2arch:459:in `gen_pkgbuild'
        from /usr/bin/gem2arch:517:in `create_packages'
        from /usr/bin/gem2arch:544:in `<main>'