Use port from PORT env variable if available (#502)

packages/server/src/cli.ts

@@ -25,7 +25,7 @@ commander.version(process.env.VERSION || "development")
 	.option("--data-dir <value>", "DEPRECATED: Use '--user-data-dir' instead. Customize where user-data is stored.")
 	.option("-h, --host <value>", "Customize the hostname.", "0.0.0.0")
 	.option("-o, --open", "Open in the browser on startup.", false)
-	.option("-p, --port <number>", "Port to bind on.", 8443)
+	.option("-p, --port <number>", "Port to bind on.", parseInt(process.env.PORT, 10) || 8443)
 	.option("-N, --no-auth", "Start without requiring authentication.", undefined)
 	.option("-H, --allow-http", "Allow http connections.", false)
 	.option("-P, --password <value>", "Specify a password for authentication.")