Update certificate-rotation.md

Added a space after "curl https://{apiserver-fqdn} -k -v 2>&1 | grep expire" for better cosmetic

Author: AndreiBarbu95

articles/aks/certificate-rotation.md

@@ -54,7 +54,7 @@ Microsoft maintains all certificates mentioned in this section, except for the c
 * Check the expiration date of the API server certificate using the following `curl` command.
 
     ```console
-    curl https://{apiserver-fqdn} -k -v 2>&1 |grep expire
+    curl https://{apiserver-fqdn} -k -v 2>&1 | grep expire
     ```
 
 ### Check VMAS agent node certificate expiration date