Fixing a minor typo in the installation docs

Update databases.md

Merge branch 'fix-404-json-file' of https://github.com/hiroponz/gitlabhq into hiroponz-fix-404-json-file

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.