set mysql image version to 5.7

5.8 changed some defaults and does not work for us at the moment

Author: David Baum

evaluationserver/docker-compose.yml

@@ -1,7 +1,7 @@
 version: "3"
 services:
     db:
-        image: mysql
+        image: mysql:5.7
         environment:
             MYSQL_ROOT_PASSWORD: dbpassword_for_user
             MYSQL_DATABASE: eval_server_development
@@ -20,4 +20,4 @@ services:
             - db
 volumes:
   bundle:
-    driver: local
+    driver: local