change the format of the build name to better work with ordering
change the format of the build name to better work with ordering

Previously, cronner's name would be `cronner-linux-amd64-3efe8b51-tbn35` when building. Now, with this change, it will look like this: `cronner-linux-amd64-tbn35-3efe8b51`. By putting the travis build number (`tbn`) first, ordering by filename should also order them by build number.

PagerDuty/cronner