Ensures that parse_all deals with an array.

# Why?
If a request returns a single object, but arkenstone was expecting an array, this will cause problems. Arkenstone iterates on all elements of what is returned by a response. If this is a plain object, that means all the keys of a hash.

# What Changed?
If a single object is sent to `parse_all`, it is put into an array, and then parsed.