gem install is hanging, it’s most likely a network, proxy, or firewall issue on your end.
You can investigate by issuing your gem install command in verbose mode with
-V. It’ll show you what URLs it’s communicating with to download the gem, and you can hopefully see what it’s doing and where it’s hanging:
> gem install -V middleman HEAD https://rubygems.org/latest_specs.4.8.gz 302 Moved Temporarily HEAD https://s3.amazonaws.com/production.s3.rubygems.org/latest_specs.4.8.gz 200 OK GET https://rubygems.org/latest_specs.4.8.gz 302 Moved Temporarily GET https://s3.amazonaws.com/production.s3.rubygems.org/latest_specs.4.8.gz ...
You can also check status.rubygems.org where they’ll alert you in case the gem/spec servers do have problems (see screenshot below):