Merge pull request #3875 from rjackson/fix_propertyBraceExpansion_prototype_expansion

[FEATURE propertyBraceExpansion] Ensure __ember_observes__ is set properly.
[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.

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`.