Use MultiJSON #dump and #load rather than #encode and #decode

MultiJSON deprecated these methods in 1.3.0 in favour of the new ones.
This requires an update to the gemspec to ensure ~>1.3

lib/fog/clodo/models/compute/server.rb

@@ -121,7 +121,7 @@ module Fog
             %{mkdir .ssh},
             %{echo "#{public_key}" >> ~/.ssh/authorized_keys},
             %{passwd -l #{username}},
-            %{echo "#{MultiJson.encode(attributes)}" >> ~/attributes.json},
+            %{echo "#{MultiJson.dump(attributes)}" >> ~/attributes.json},
           ])
         rescue Errno::ECONNREFUSED
           sleep(1)