fix capitalization

Author: GitHubber17

articles/security/fundamentals/TOC.yml

@@ -99,7 +99,7 @@
     href: virtual-machines-overview.md
   - name: Best practices - IaaS workloads
     href: iaas.md
-  - name: Azure marketplace images
+  - name: Azure Marketplace images
     href: azure-marketplace-images.md
 
 - name: Data security, encryption, and storage
@@ -183,4 +183,4 @@
   - name: Pen testing
     href: pen-testing.md
   - name: Azure domains
-    href: azure-domains.md
+    href: azure-domains.md