Correct usage of formatName() function in docs (#8122)

The code section above these changes defines a `formatName` function
that expects a parameter `user`. The code section containing these
changes incorrectly called `formatName(user.name)`. For those following
along with CodePen, this section should correctly call
`formatName(user)`.

docs/introducing-jsx.md

@@ -59,7 +59,7 @@ This means that you can use JSX inside of `if` statements and `for` loops, assig
 ```js{3,5}
 function getGreeting(user) {
   if (user) {
-    return <h1>Hello, {formatName(user.name)}!</h1>;
+    return <h1>Hello, {formatName(user)}!</h1>;
   } else {
     return <h1>Hello, Stranger.</h1>;
   }