add mysql to nginx network group

Docker/mysql/docker-compose.yml

@@ -11,4 +11,12 @@ services:
       - MYSQL_ROOT_PASSWORD=wEskwd0CvRH7
     ports:
       - 3090:3306
-    image: mysql:5.7
+    image: mysql:5.7
+    networks:
+      nginx:
+        aliases:
+          - mysql
+
+networks:
+  nginx:
+    external: true