chore: modify CONTRIBUTING.md (#2599)

Author: evilebottnawi

CONTRIBUTING.md

@@ -31,7 +31,7 @@ Run the relevant [examples](https://github.com/webpack/webpack-dev-server/tree/m
 
 Once it is done, you can modify any file locally. In the `examples/` directory you'll find a lot of examples with instructions on how to run it. This can be very handy when testing if your code works.
 
-If you are modifying a file in the `client/` directory, be sure to run `npm run prepublish` after it. This will recompile the files.
+If you are modifying a file in the `client/` directory, be sure to run `npm run build:client` after it. This will recompile the files.
 
 ## Testing a Pull Request