How to fix "Error: Could not find the implementation for builder @angular-devkit/build-angular:dev-server"

How to fix "Error: Could not find the implementation for builder @angular-devkit/build-angular:dev-server"

我将我的 angular 项目升级到 angular 8，现在当我输入 

ng serve

我收到此错误：

Error: Could not find the implementation for builder @angular-devkit/build-angular:dev-server

升级我使用了ng update。当我输入 

ng update

我得到：

Using package manager: 'npm'

Collecting installed dependencies...

Found 41 dependencies.

We analyzed your package.json and everything seems to be in order. Good work!

也许这会有所帮助

npm install --save-dev @angular-devkit/build-angular