fix formatting error in external kdu_compress command

Signed-off-by: Sebastian Schüpbach <sebastian.schuepbach@unibas.ch>
3 jobs for master in 12 minutes and 50 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed test #42700
mbr

00:03:44

 
  Build
passed assembly #42701
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00:02:01

 
  Publish
passed master-branch-image #42702

00:07:04