Update instance-metadata-service.md

Fix PowerShell command label

Author: paulmey

articles/virtual-machines/linux/instance-metadata-service.md

@@ -540,7 +540,7 @@ The signature blob is a [pkcs7](https://aka.ms/pkcs7) signed version of document
 
 Instance metadata can be retrieved in Windows via the PowerShell utility `curl`:
 
- ```bash
+ ```powershell
 curl -H @{'Metadata'='true'} "http://169.254.169.254/metadata/attested/document?api-version=2018-10-01&nonce=1234567890" | select -ExpandProperty Content
 ```