updates command-palette example to fix SSR (adobe#8638)

Author: souporserious

packages/react-aria-components/docs/examples/command-palette.mdx

@@ -66,7 +66,13 @@ function CommandPaletteExample() {
 
   let [isOpen, setOpen] = useState(false);
   let {contains} = useFilter({sensitivity: 'base'});
-  let isMac = useMemo(() => /Mac/.test(navigator.platform), []);
+  let isMac = useMemo(
+    () =>
+      typeof navigator === 'undefined'
+        ? false
+        : /mac(os|intosh)/i.test(navigator.userAgent),
+    []
+  )
 
   useEffect(() => {
     const handleKeyDown = (e) => {