fix for --cycle with a cycle time specified.

Fix for:

"
    [ ... ]
       # Force task to always run at 0z:
       environment scripting = "eval $(rose task-env --cycle=$(rose date --print-format="%Y%m%d00" ${CYLC_TASK_CYCLE_TIME}))"
 
However, this fails with the following error:

  JOB SCRIPT STARTING
  [FAIL] days=-2013030700; must have magnitude <= 999999999
"