Typo in defining the client chapter

Adding the code in `Defining the client' in the project resulted in project errors due to misalignments between the code and what was documented

IdentityServer/v7/docs/content/quickstarts/1_client_credentials.md

@@ -147,7 +147,7 @@ Add this client definition to *Config.cs*:
 
 ```cs
 public static IEnumerable<Client> Clients =>
-    new Client
+    new Client[]
 
     {
         new Client