Fix dangling comma

containers/dotnetcore/.devcontainer/devcontainer.json

@@ -20,7 +20,7 @@
 	// Add the IDs of extensions you want installed when the container is created.
 	"extensions": [
 		"ms-dotnettools.csharp"
-	],
+	]
 
 	// Use 'forwardPorts' to make a list of ports inside the container available locally.
 	// "forwardPorts": [5000, 5001],