Fix branch detection for automated hatchet tests (#565)

etc/hatchet.sh

@@ -31,7 +31,7 @@ elif [ -n "$TRAVIS_PULL_REQUEST_BRANCH" ]; then
   export IS_RUNNING_ON_TRAVIS=true
   export HATCHET_BUILDPACK_BRANCH="$TRAVIS_PULL_REQUEST_BRANCH"
 else
-  export HATCHET_BUILDPACK_BRANCH=$(git name-rev HEAD 2> /dev/null | sed 's#HEAD\ \(.*\)#\1#')
+  export HATCHET_BUILDPACK_BRANCH=$(git name-rev HEAD 2> /dev/null | sed 's#HEAD\ \(.*\)#\1#' | sed 's#tags\/##')
 fi
 
 gem install bundler