update markdown tests (#7838)

update markdown tests

  - explicitly use gulp 4.0 beta because 3.9 depends on a vulnerable package

docs/cmdlet-example/command-line-simple-example.md

@@ -186,16 +186,19 @@ If you copy `netstandard.dll` from this directory to the directory containing
    get it to reload `MyModule.dll`.
 
 1. Copy the `netstandard.dll` implementation assembly for .NET 4.6.1 to the module's directory.
+
    ```powershell
    cd 'path-to-where-you-copied-module.dll'
    Copy-Item 'C:\Program Files\dotnet\sdk\<version-number>\Microsoft\Microsoft.NET.Build.Extensions\net461\lib\netstandard.dll' .
    ```
 
 1. Import the module and execute the command:
+
    ```powershell
    Import-Module .\MyModule.dll
    Write-TimestampedMessage "Test message."
    ```
+
    Now the command should succeed.
 
    Note: If it fails, restart Windows PowerShell to make sure

docs/maintainers/best-practice.md

@@ -17,13 +17,13 @@
 
 - Use `Squash and merge` by default to keep clean commit history in Master branch.
 
-  ![](./Images/squash-merge.png)    ![](./Images/squash-confirm.png)
+  ![Squash Merge Example](./Images/squash-merge.png)    ![Squash Confirm Example](./Images/squash-confirm.png)
 
 - Use `Create a merge commit` for feature-work PRs **only if** the commit history of the PR is reasonably clean.
   After using this option, GitHub will make it your default option for merging a PR.
   Do remember to change the default back to `Squash and merge`.
 
-  ![](./Images/merge-commit.png)    ![](./Images/merge-commit-confirm.png)
+  ![Merge Commit Example](./Images/merge-commit.png)    ![Merge Confirm Example](./Images/merge-commit-confirm.png)
 
 - Avoid `Rebase and merge` unless you have a strong argument for using it.