Use fivemat as default rspec formatter.

Optional pull request, I much prefer this as a default formatter for specs. It gives me a better overview of where my tests are and how much time is being spent on them, especially as the number of tests in your project grows.

For individual spec runs I will often pass `--format documentation` on the command line.

Output now looks like this:

```
Cart . (0.04s)
Product ........ (0.79s)
AddLineItemService ......... (0.1s)
Categorization .... (0.05s)
CartsController .. (0.09s)
Category .. (0.03s)
AdminController .. (0.1s)
ProductsController ......* (0.08s)
LineItem .... (0.01s)
CategoriesController ....... (0.08s)
LineItemsController .*......... (0.26s)

Pending:
  ProductsController#create successfully Can't stub out the join table, params is nil and breaks shit
    # No reason given
    # ./spec/controllers/products_controller_spec.rb:36
  LineItemsController#destroy the line item quantity is greater than 1 should decrement the line item quantity
    # How can I update an attribute without using a model/factory?
    # ./spec/controllers/line_items_controller_spec.rb:106

Finished in 1.7 seconds
57 examples, 0 failures, 2 pending

Randomized with seed 60247
```

Be sure to add `export FIVEMAT_PROFILE=1` to your `.bash_profile` to get the timing output.