Use Docker Compose specification

docker-compose.nginx.yml

@@ -1,5 +1,3 @@
-version: "2.4"
-
 services:
   nginx:
     depends_on:

docker-compose.without-nginx.yml

@@ -1,5 +1,3 @@
-version: "2.4"
-
 services:
   mattermost:
     ports:

docker-compose.yml

@@ -1,7 +1,4 @@
 # https://docs.docker.com/compose/environment-variables/
-
-version: "2.4"
-
 services:
   postgres:
     image: postgres:${POSTGRES_IMAGE_TAG}