message: Update installing-autorest.md to correct outdated information
diff: Installing AutoRest on Windows, MacOS or Linux involves two steps:
  -1. __Install [Node.js](https://nodejs.org/en/)__ (10.15.x LTS preferred. May not function with Node < 10.x Be Wary of 11.x builds as they may introduce instability or breaking changes. )
  +1. __Install [Node.js](https://nodejs.org/en/)__ (12.19.x LTS preferred. May not function with Node < 10.x.)
  > if you want an easy way to install and update Node, I recommend [NVS - Node Version Switcher](./nodejs/installing-via-nvs.md) or [NVM - Node Version Manager](./nodejs/installing-via-nvm.md)
  @@ -15,15 +15,6 @@ Installing AutoRest on Windows, MacOS or Linux involves two steps:
  # run using command 'autorest'
  autorest --help
  ```
  -Or the beta version of AutoRest v3, side-by-side:
  -
  - ``` powershell
  - # Depending on your configuration you may need to be elevated or root to run this. (on OSX/Linux use 'sudo' )
  - npm install -g @autorest/autorest
  -
  - # run using command 'autorest-beta'
  - autorest-beta --help
  - ```
  ### Updating Autorest core
  To update AutoRest if you have previous versions installed, please run:
  