docker-compose: using latest mysql 5.x docker image instead of latest

Change-Id: I9dbfde56d3733d09bf97a5e5c0277614fea633f8
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/docker/docker-compose.yaml b/docker/docker-compose.yaml
index d6579ab..da1d16e 100644
--- a/docker/docker-compose.yaml
+++ b/docker/docker-compose.yaml
@@ -1,7 +1,7 @@
 version: '2'
 services:
   osm-ro-db:
-    image: mysql
+    image: mysql:5
     container_name: osm-ro-db
     restart: always
     environment: