helmholtz-marketplace-app: use image instead of object tag


- substitute the image tag for the object tag
5 jobs for master in 1 minute and 57 seconds (queued for 2 seconds)
Name Stage Failure
test Test
[ERROR] Failed to execute goal com.github.eirslett:frontend-maven-plugin:1.9.1:karma (unit and integration tests) on project helmholtz-marketplace-webapp: Failed to run task: 'karma start karma.conf.js' failed. org.apache.commons.exec.ExecuteException: Process exited with an error: 1 (Exit value: 1) -> [Help 1]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException
Cleaning up file based variables
ERROR: Job failed: exit code 1