Use version for the MySQL image to avoid issues with caching_sha2_password (#533)

docker/docker-compose.prod.yml

@@ -1,7 +1,7 @@
 version: '2'
 services:
     database:
-        image: mysql
+        image: mysql:5.7
         environment:
         - MYSQL_ROOT_PASSWORD=${DB_ROOT_PASSWORD}
         - MYSQL_DATABASE=${DB_NAME}

docker/docker-compose.yml

@@ -1,7 +1,7 @@
 version: '2'
 services:
     database:
-        image: mysql
+        image: mysql:5.7
         environment:
         - MYSQL_DATABASE=${DB_NAME}
         - MYSQL_USER=${DB_USERNAME}