Update ruby to latest version.

Change gollum repo to use https:// instead of git://

Attribution as mentioned in https://news.ycombinator.com/item?id=5423635

A lot of people might have firewalls blocking the git:// protocol. Using https:// makes this easier and matches the other git repositories in the Gemfile.

Fix style of network graph.

It is easy to see which branch is merged.

refs #3258