Fix syntax error in older rubies

Author: jackfranklin

spec/client_spec.rb

@@ -134,7 +134,7 @@
           stub_request(:get, api_path).to_return({
             :status => 200,
             :body => MultiJson.encode({
-              'users': [{ 'id' => 1 }]
+              'users' => [{ 'id' => 1 }]
             })
           })
           expect(@client.channel_users('mychannel')).to eq({