Semi-hotfix for Rails configuration bug
Semi-hotfix for Rails configuration bug

At the time Bundler loads NullDB, Rails.root will return nil. We need to
defer calling Rails.root until after Rails loads; would be nice to not
redefine Configuration#project_root, but that does work.

Would not be an issue if people were required to put
`require 'nulldb/rails'` in their projects, perhaps the solution is
moving towards that.

Closes #16

theironyard/nulldb,avdi/nulldb,nulldb/nulldb,nickahoy/nulldb,Sirupsen/nulldb,blaet/nulldb,envato/nulldb,voxik/nulldb