docs(@angular-devkit/build-angular): remove ="true" from prod flag in ng build documentation

(cherry picked from commit a75478a)

Author: alan-agius4

packages/angular/cli/commands/build-long.md

@@ -3,7 +3,7 @@ When used to build a library, a different builder is invoked, and only the `ts-c
 All other options apply only to building applications.
 
 The application builder uses the [webpack](https://webpack.js.org/) build tool, with default configuration options specified in the workspace configuration file (`angular.json`) or with a named alternative configuration.
-A "production" configuration is created by default when you use the CLI to create the project, and you can use that configuration by specifying the `--configuration="production"` or the `--prod="true"` option.
+A "production" configuration is created by default when you use the CLI to create the project, and you can use that configuration by specifying the `--configuration="production"` or the `--prod` option.
 
 The configuration options generally correspond to the command options.
 You can override individual configuration defaults by specifying the corresponding options on the command line.