Bump Ruby to 2.1.3
Bump Rails to 4.2.0.beta2

- Sprockets now requires a .css.sass extension
  (but not Sass, so included filed don’t need it)
- friendly_id needs `.friendly` when `.find`ing (they say they’ll fix this)
- Devise needed an update
- simple_form is on master to fix Rails 5 deprecation warning