Ensure slurp keys are symbolized

[jamesdphillips]

If the parameter's key is not a symbol the path cannot be built.

Ex.

class User < JsonApiClient::Resource
  belongs_to :organization
end 

user = User.create("id" => 12, "organization_id" => 10, "name" => "Gob Bluth")
#=> Exception, "Not all prefix parameters specified"

user = User.create(params.require(:user).permit(:id, :organization_id, :name))
#=> Exception, "Not all prefix parameters specified"

The exception is thrown on line 35, in the example it equates to:
"/organizations/%{id}/users" % { "organization_id" => 12 } #=> KeyError: key{organization_id} not found

[chingor13]

Can you put the failing case into a test so we can ensure it won't happen again if a refactor happens?

[chingor13]

whoops, merged this accidentally. but merged in #27 which fixes this issue