Add missing space to console.log message about flushing stats.

The current behavior results in the following log message:

`25 Mar 16:36:09 - Flushing stats atTue Mar 25 2014 16:36:09 GMT+0000 (UTC)`

This change represents a very minor tweak, to make the log message slightly nicer:

`25 Mar 16:36:09 - Flushing stats at Tue Mar 25 2014 16:36:09 GMT+0000 (UTC)`