chore: allow dynamic set port

vue.config.js

@@ -7,10 +7,13 @@ function resolve(dir) {
 }
 
 const name = defaultSettings.title || 'vue Element Admin' // page title
+
 // If your port is set to 80,
 // use administrator privileges to execute the command line.
 // For example, Mac: sudo npm run
-const port = 9527 // dev port
+// You can change the port by the following method:
+// port = 9527 npm run dev OR npm run dev --port = 9527
+const port = process.env.port || process.env.npm_config_port || 9527 // dev port
 
 // All configuration item explanations can be find in https://cli.vuejs.org/config/
 module.exports = {