Remove `length` property in favor of `duration`.

In JSON, consider `length` a reserved word which can only be used to
refer to the number of iterable keys in an array-like object.

https://github.com/angular/angular.js/blob/master/src/Angular.js#L185
The current behavior causes stories with a zero duration to have no
properties copied from the JSON response because Angular detects them
as array-like and having no properties.

Also bumps to a newer version of guard-minitest.
Merge pull request #33 from PRX/fix/length_is_reserved

Remove `length` property in favor of `duration`.
fixing story routes
switch to minitest-spec-rails, which seems to actually work pretty well
Fall back on series image for missing story image.
get factory_girl helpers in tests
Merge pull request #34 from PRX/fix/test_runner

switch to minitest-spec-rails, which seems to actually work pretty well
add profile to representer
merge branch master
Merge pull request #35 from PRX/feat/story_default_series_image

Fall back on series image for missing story image.
Merge branch 'master' into picks
updating schema and adding tests for picks and pick lists and updating root api representer to include staff picks