Update .gitlab-ci.yml fixed typo in centOS image name.

.gitlab-ci.yml

 makefile_generation_and_compilation_plus_run_nrt_tests_cluster:
-    image: registry-gitlab.pasteur.fr/dsi-tools/docker-images:centos7-rock
+    image: registry-gitlab.pasteur.fr/dsi-tools/docker-images:centos7_rock
     script: 
         - source /etc/profile.d/gensoft_modules.sh 
         - ls /etc/profile.d
@@ -18,4 +18,4 @@ makefile_generation_and_compilation_plus_run_nrt_tests_cluster:
         - cd ..; make check
         
 
-    
\ No newline at end of file
+