refactor: remove redundant fragment (#309)

Author: noritaka1166

src/theme/DocItem/index.js

@@ -2,9 +2,5 @@ import React from 'react';
 import DocItem from '@theme-original/DocItem';
 
 export default function DocItemWrapper(props) {
-  return (
-    <>
-      <DocItem {...props} />
-    </>
-  );
+  return <DocItem {...props} />;
 }