docs(customize/theme): fix example code in Option 2 section

Author: tulup-conner

app/docs/customize/theme/theme.mdx

@@ -51,7 +51,7 @@ const customTheme: CustomFlowbiteTheme = {
 
 export default function MyPage() {
   return (
-    <Flowbite theme={customTheme}>
+    <Flowbite theme={{ theme: customTheme }}>
       <Button color="primary">Click me</Button>
     </Flowbite>
   );