[Linux] Update Ubuntu in WSL

As there is no latest version (20.10) in Microsoft Store, For updating WSL Ubuntu to latest version, it need to do it by ourselves.

Steps as below.

1. Change default upgrade behavior settings.
   Execute command below and change Prompt to normal then input Ctrl-X to exit.

   sudo vi /etc/update-manager/release-upgrades

   

2. Upgrade current release to latest version to ensure it can detect latest Ubuntu.
   Execute command below.

   ## Refetch repo settings.
   sudo apt-get update -qq
   
   ## Refetch package.
   sudo apt-get upgrade -qq
   
   ## Update OS.
   sudo do-release-upgrade