Typo in powershell command

[chunsiongtan]

Get-AzureRmApplicationGatewayFrontendIPort is no a valid command
Get-AzureRmApplicationGatewayFrontendPort proposed as the corrected powershell command

Description

Checklist

• I have read the Submitting Changes section of CONTRIBUTING.md
• The title of the PR is clear and informative
• The appropriate change log has been updated
• 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:
  • the changes have gone through a cmdlet design review
  • the cmdlet markdown files were generated using the platyPS module

[cormacpayne]

@chunsiongtan thank you for all of the doc updates 😀