Entrypoint.sh: use common way to execute argument given

This fixes issue #8 (#8 ), where the previous way resulted in a failure with gitlab's CI. (see e.g. https://gitlab.com/gitlab-org/gitlab-runner/issues/1253)

Author: JohanEngelen

entrypoint.sh

@@ -12,5 +12,5 @@ if [ "${USER_ID}" -ne "0" ]; then
 
   /usr/local/bin/gosu ${USER_NAME} /bin/bash -c "${CMD}"
 else
-  /bin/bash -c "${CMD}"
+  exec "$@"
 fi