Merge branch 'master' of git.lsh.uni-kiel.de:opendata/dcat-catalogy-proxy

.gitlab-ci.yml

+variables:
+  MAVEN_OPTS: "-Dmaven.repo.local=.m2/repository -Dorg.slf4j.simpleLogger.log.org.apache.maven.cli.transfer.Slf4jMavenTransferListener=WARN -Dorg.slf4j.simpleLogger.showDateTime=true -Djava.awt.headless=true"
+  MAVEN_CLI_OPTS: "--batch-mode --errors --fail-at-end --show-version -DinstallAtEnd=true -DdeployAtEnd=true"
+
+cache:
+  paths:
+    - .m2/repository
+
+test:
+  image: maven:3-openjdk-11
+  stage: test
+  script: 
+    - mvn --no-transfer-progress test