Change DATABASE_URL

Use password set by the POSTGRES_PASSWORD variable

source/docker.sample.env

@@ -14,7 +14,7 @@ POSTGRES_USER=plume
 POSTGRES_DB=plume
 
 # you can safely leave those defaults
-DATABASE_URL=postgres://plume:plume@postgres:5432/plume
+DATABASE_URL=postgres://plume:passw0rd@postgres:5432/plume
 MIGRATION_DIRECTORY=migrations/postgres
 USE_HTTPS=1
 ROCKET_ADDRESS=0.0.0.0