Update webpack-dev-server.md docs (#2712)

The dev_server parts now only apply when running the webpack-dev-server.

Author: justin808

docs/webpack-dev-server.md

@@ -14,7 +14,7 @@ in your console, simply open the link in your browser and accept the SSL excepti
 Now if you refresh your Rails view everything should work as expected.
 
 
-## HOT module replacement
+## Hot Module Replacement
 
 Webpacker out-of-the-box supports HMR with `webpack-dev-server` and
 you can toggle it by setting options in `config/webpacker.yml`:
@@ -38,10 +38,6 @@ Check out this guide for more information:
 
 To support HMR with React, see [docs/react.md](./react.md#hmr-and-react-hot-reloading).
 
-**Note:** Don't forget to disable `HMR` if you are not running `webpack-dev-server`
-otherwise you will get not found error for stylesheets.
-
-
 ## Nginx
 
 If you use Nginx in development to proxy requests to your Rails server from