[BUGFIX beta] Update to latest `ember-dev`.

* Updates to the latest `ember-dev` which ensures that the `git config
  user.name` and `git config user.email` values are present before calling
  `git cherry-pick`. This is due to a recent change in git `1.8.5` which
  requires the user information be present prior to a cherry-pick.
* Updates to bundler `1.5.0.rc1` to use the following features:
  * Automatically retry 3 times (should help with gem installation failures
    in Travis).
  * Install gems in parallel (use 4 workers by default).
* Forces each branch to be tested independently (prevents a resource
  contention issue when checking out another branch in the same test
  run).
* Travis accidentally reverted to using an older git version that does not
  support the `--points-at` flag that we are using in `ember-dev`.  This
  forces the system to upgrade to the latest version.

Travis ticket for reference:
  https://github.com/travis-ci/travis-ci/issues/1710.
[BUGFIX beta] Ensure features are tested by Travis.

 #3635 caused the Travis builds to use the `enableallfeatures` flag to
 enable features, but this was changed in `ember-dev` (and updated in
 Ember in #3633) to `enableoptionalfeatures`.