Allow user to specify port

.env.docker

@@ -21,7 +21,7 @@ TRUSTED_PROXIES=${TRUSTED_PROXIES}
 # If you use SQLite, set connection to `sqlite` and remove the database, username and password settings.
 DB_CONNECTION=mysql
 DB_HOST=${FF_DB_HOST}
-DB_PORT=3306
+DB_PORT=${FF_DB_PORT}
 DB_DATABASE=${FF_DB_NAME}
 DB_USERNAME=${FF_DB_USER}
 DB_PASSWORD=${FF_DB_PASSWORD}
@@ -88,4 +88,4 @@ DEMO_PASSWORD=
 IS_DOCKER=true
 IS_SANDSTORM=false
 IS_HEROKU=false
-TZ=${TZ}
+TZ=${TZ}