Update docker image for staging

src/main/docker/gitsearch.yml

 version: '3.5'
 services:
   gitsearch-app:
-    image: docker.uibk.ac.at:443/csar9407/gitsearch:development-8c73612a7c7caddaa05981097d66096eb815cc2d
+    image: docker.uibk.ac.at:443/csar9407/gitsearch:staging-3c2e4895e32dd72aa90f64d7ec7584d656f4d18b
     container_name: sharing_search
     environment:
       - _JAVA_OPTIONS=-Xmx512m -Xms256m