Cave in and put the image on docker hub.

This is needed so the gitlab runner from the gorlatch group can find it.

.gitlab-ci.yml

@@ -17,6 +17,6 @@ before_script:
 - ( cd dune/perftool/vectorclass && git apply ../../../patches/vectorclass/*.patch )
 
 debian:9--gcc:
-  image: registry.jorrit.de/perftools-ci:9
+  image: exbart/perftools-ci:9
   script:
     bin/duneci-perftool-small-test