The integration spec runner should run `rake`
Fix test runner bug which won't update bundle

* Consider this scenario: _tmp directory holds a particular version of
 cucumber/cucumber and some commits were made to the remote of
 cucumber-ruby-core. Now, after running git pull in the
 cucumber-ruby-core repo to fetch the latest changes, running the
 integration tests would fail since the Gemfile.lock inside
 cucumber/cucumber stores a particular commit SHA from the previous run
 of integration spec.

* To get around this issue, `bundle update cucumber-ruby-core` inside
 cucumber/cucumber should be run after pulling the changes in
 cucumber-ruby-core. But this will fail if `bundle install` is not run
 in the first place. So, the script would check for the presence of
 Gemfile.lock and run `bundle update` or `bundle install` accordingly.