ci: version is obsolete in docker-compose.yml (#1167)

Author: n-rodriguez

docker-compose.yml

@@ -1,4 +1,3 @@
-version: '3.9'
 services:
   postgres:
     image: postgres:10
@@ -7,9 +6,10 @@ services:
       POSTGRES_DB: acts_as_taggable_on
       POSTGRES_PASSWORD: postgres
     ports: ['5432:5432']
+
   mysql:
     image: mysql:8
     environment:
       MYSQL_ALLOW_EMPTY_PASSWORD: true
       MYSQL_DATABASE: acts_as_taggable_on
-    ports: ['3306:3306']
+    ports: ['3306:3306']