refactored tag management

2 jobs for nginx/1.13-1 in 20 seconds
latest
Name Stage Failure
failed
nginx_image Image There is an unknown failure, please try again
 ---> Running in 44e9219c1659
Removing intermediate container 44e9219c1659
---> 1000a689eb40
Step 7/7 : ADD assets/nginx.conf /etc/nginx/conf.d/default.conf
---> 998ce18028e8
Successfully built 998ce18028e8
Successfully tagged services.ub.uni-leipzig.de:11443/bdd_dev/vufind/nginx:1.13-1
invalid reference format
ERROR: Job failed: exit code 1