Bump .ruby-version to 2.1.2
Merge pull request #324 from alphagov/upgrade-ruby-to-2.1.2

Bump .ruby-version to 2.1.2
Allow site import to move hosts between sites

This is useful when we want to split some hosts to a new site.
Clear hit-mapping relationships when moving between sites

If a host is moved between sites, it's Hits and HostPaths no longer belong to
that site.