Revert "Revert "Fix environment timezone""

This reverts commit b7d0323afa.

docker-compose.nginx.yml

@@ -23,7 +23,7 @@ services:
       - shared-webroot:/usr/share/nginx/html
     environment:
       # timezone inside container
-      - TZ
+      - TZ: ${TZ}
     ports:
       - ${HTTPS_PORT}:443
       - ${HTTP_PORT}:80

docker-compose.yml

@@ -18,7 +18,7 @@ services:
       - ${POSTGRES_DATA_PATH}:/var/lib/postgresql/data
     environment:
       # timezone inside container
-      - TZ
+      - TZ: ${TZ}
 
       # necessary Postgres options/variables
       - POSTGRES_USER
@@ -45,7 +45,7 @@ services:
       - ${MATTERMOST_CLIENT_PLUGINS_PATH}:/mattermost/client/plugins:rw
     environment:
       # timezone inside container
-      - TZ
+      - TZ: ${TZ}
 
       # necessary Mattermost options/variables (see env.example)
       - MM_SQLSETTINGS_DRIVERNAME