Add abbr attribute to Linode DataCenter.

lib/fog/linode/models/compute/data_center.rb

@@ -6,6 +6,7 @@ module Fog
       class DataCenter < Fog::Model
         identity :id
         attribute :location
+        attribute :abbr
       end
     end
   end

tests/linode/requests/compute/datacenter_tests.rb

@@ -3,7 +3,8 @@ Shindo.tests('Fog::Compute[:linode] | datacenter requests', ['linode']) do
   @datacenters_format = Linode::Compute::Formats::BASIC.merge({
     'DATA' => [{
       'DATACENTERID'  => Integer,
-      'LOCATION'      => String
+      'LOCATION'      => String,
+      'ABBR'          => String
     }]
   })