Bump rspec to ~> 2.12.0 in test_app

Otherwise, on a fresh rvm install the test_app pulls in rspec 2.0.1
which fails with "undefined method `run_all' for []:Array" when
running tests in the test_app with ruby 1.9.3.
Merge pull request #527 from steffengodskesen/bump_rspec_to_2_12_in_test_app

Bump rspec to ~> 2.12.0 in test_app