message: Fix stable version command name in installation doc
diff: @@ -13,7 +13,7 @@ Installing AutoRest on Windows, MacOS or Linux involves two steps:
  npm install -g autorest
  # run using command 'autorest'
  - autorest-beta --help
  + autorest --help
  ```
  Or the beta version of AutoRest v3, side-by-side:
  