updated Az.WebApp

[inmishrar]

4.6.2 - August 2020

Az.WebApp

• Added '-dotnetcore' to Set-AzWebApp' to update runtime stack of Azure Web App to dotnetcore [[Aks] update api version to 2020-06-01 #12883]

Checklist

• I have read the Submitting Changes section of CONTRIBUTING.md
• The title of the PR is clear and informative
• The appropriate ChangeLog.md file(s) has been updated:
  • For any service, the ChangeLog.md file can be found at src/{{SERVICE}}/{{SERVICE}}/ChangeLog.md
  • A snippet outlining the change(s) made in the PR should be written under the ## Upcoming Release header -- no new version header should be added
• The PR does not introduce breaking changes
• If applicable, the changes made in the PR have proper test coverage
• For public API changes to cmdlets:
  • a cmdlet design review was approved for the changes in this repository (Microsoft internal only)
  • the markdown help files have been regenerated using the commands listed here

[msJinLei]

@inmishrar Thanks for your contribution. You don't need to update changelog.md. We will merge the #12833 when review is finished. We are closing this pr now.