docs(getting-started): revise references to cli

Official name of cli is Angular CLI and the npm package is now @angular/cli

Author: andrewseguin

guides/getting-started.md

@@ -1,9 +1,9 @@
 Get started with Angular Material using the Angular CLI.
 
-## Install the CLI
+## Install Angular CLI
 
  ```bash
- npm install -g angular-cli
+ npm install -g @angular/cli
  ```
 
 ## Create a new project