build_detector.sh: clone into a predictable url
$JUGGLER_DETECTOR_REPOSITORYURL may not be called the same name as $JUGGLER_DETECTOR
Should help with https://github.com/eic/epic/pull/17
$JUGGLER_DETECTOR_REPOSITORYURL may not be called the same name as $JUGGLER_DETECTOR
Should help with https://github.com/eic/epic/pull/17