Remove the 'Z' from TimeStamp for TeamCity runner

Following off of the same fix here, https://github.com/pifantastic/teamcity-service-messages/pull/10 we need to remove the trailing Z from the time stamp for TeamCity to process the service messages. Otherwise we get the following error in TeamCity version 8.1.5:

Unparseable date: "2014-10-13T17:29:39.747Z"