make resolver accessible
implement specs for run_on_modifications
implement correct logic for failing tests

Teaspoon’s console#execute_without_handling method returns true if all
specs pass and false if one doesn’t. This commit contains changes to
apply to this contract.
update Gemfile to match the versions teaspoon is using
add spring to Gemfile
Merge pull request #32 from samu/master

implement specs for run_on_modifications and make specs pass