运行npm run ng时，编译成功，但是出现以下错误，并且浏览器显示Not found消息。
[rendered]
ℹ ｢wdm｣: Compiled successfully.
(node:31294) UnhandledPromiseRejectionWarning: Error: Exited with code 3
at ChildProcess.cp.once.code (/home/itadmin/my-
website/node_modules/@angular-devkit/build-
angular/node_modules/opn/index.js:84:13)
at Object.onceWrapper (events.js:273:13)
at ChildProcess.emit (events.js:182:13)
at maybeClose (internal/child_process.js:961:16)
at Socket.stream.socket.on (internal/child_process.js:380:11)
at Socket.emit (events.js:182:13)
at Pipe._handle.close (net.js:598:12)
(node:31294) UnhandledPromiseRejectionWarning: Unhandled promise rejection.
This error originated either by throwing inside of an async function without
a catch block, or by rejecting a promise which was not handled with
.catch(). (rejection id: 14)
(node:31294) [DEP0018] DeprecationWarning: Unhandled promise rejections are
deprecated. In the future, promise rejections that are not handled will
terminate the Node.js process with a non-zero exit code.