docker-compose files: remove version

Author: jgauthi

.docker/compose/base-dev.yml

@@ -1,4 +1,3 @@
-version: '3.6'
 services:
   db:
     build:

.docker/compose/base.yml

@@ -1,4 +1,3 @@
-version: '3.6'
 services:
   web:
     image: nginx

.docker/compose/maildev.yml

@@ -1,4 +1,3 @@
-version: '3.6'
 services:
   maildev:
     image: maildev/maildev

.docker/compose/phpmyadmin.yml

@@ -1,4 +1,3 @@
-version: '3.6'
 services:
   phpmyadmin:
     image: phpmyadmin/phpmyadmin