docs: fix typos

Co-authored-by: Trivikram Kamat <[email protected]>

UPGRADING.md

@@ -237,7 +237,7 @@ Default credential provider is how SDK resolve the AWS credential if you DO NOT
   };
   const client = new FooClient({
     credentials: fromTemporaryCredentials({
-      sourceCredentials,
+      masterCredentials: sourceCredentials,
       params: { RoleArn },
     }),
   });