pin the ruby version to the latest 1.9.3

without pinning the ruby version, running `bundle exec rake spec`
uses the system ruby to run rspec, and because of [an issue in `rbenv`](https://github.com/sstephenson/rbenv/pull/372)
this doesn't work properly in the dev VM. The `rbenv` bugfix hasn't
been released as of this time.
GDS::SSO::User correctly exposes attrs for mass-assignment
Merge pull request #29 from alphagov/pin-ruby-version

pin the ruby version to the latest 1.9.3 point release
Merge pull request #30 from layam/fix-user-attr-accessible

GDS::SSO::User correctly exposes attrs for mass-assignment
bumping combustion gem version to fix build
test class extends ActiveRecord::Base

de804b25cb83f9232965aa70a06dcc177db9442b fixed the GDS::SSO:User
so that `attr_accessible` is called on various fields. However,
this assumes that `attr_accessible` is available on the user model
class (hence the test also reflects this).