My development server is behind a firewall which allows only well-known ports like ssh, http and https.
The following line in the discourse Gemfile gives me an error after long waiting.
gem 'redis-rails', :git => 'git://github.com/SamSaffron/redis-store.git'
Updating git://github.com/SamSaffron/redis-store.git github.com[0: 126.96.36.199]: errno=Connection timed out fatal: unable to connect a socket (Connection timed out)
When I change git:// to https://, it works fine.
I found the similar issue on Stack Overflow.