Wrap faraday errors
Improve API error message to be more descriptive

Raise an exception with both the original message
and the validation errors.
Handle API exceptions error messages
Fix wrongfully overriden options hash in Request#get
Fix defaults assignement in Request

Using #merge does not override options already set
Change #set_order_shipping_method to work with current Spree

The [documentation](http://api.spreecommerce.com/v1/orders/#selecting-a-delivery-method) says the `shipping_method_id` has to be on the toplevel params hash, but that's not how Spree implements it.

This change makes the call work with the current spree (1.3.2)
Specify jruby platform on json dependency
Add pry in development group