docs: add ling1726 as a contributor for code, test (#63)

Co-authored-by: allcontributors[bot] <46447321+allcontributors[bot]@users.noreply.github.com>

Author: allcontributors[bot]

.all-contributorsrc

@@ -134,7 +134,8 @@
       "avatar_url": "https://avatars.githubusercontent.com/u/20744592?v=4",
       "profile": "https://github.com/ling1726",
       "contributions": [
-        "code"
+        "code",
+        "test"
       ]
     }
   ],

README.md

@@ -175,6 +175,7 @@ Thanks goes to these people ([emoji key][emojis]):
     <td align="center"><a href="https://stackshare.io/jdorfman/decisions"><img src="https://avatars1.githubusercontent.com/u/398230?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Justin Dorfman</b></sub></a><br /><a href="#fundingFinding-jdorfman" title="Funding Finding">🔍</a></td>
     <td align="center"><a href="https://github.com/RoystonS"><img src="https://avatars0.githubusercontent.com/u/19773?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Royston Shufflebotham</b></sub></a><br /><a href="https://github.com/kentcdodds/rtl-css-js/issues?q=author%3ARoystonS" title="Bug reports">🐛</a> <a href="https://github.com/kentcdodds/rtl-css-js/commits?author=RoystonS" title="Code">💻</a> <a href="https://github.com/kentcdodds/rtl-css-js/commits?author=RoystonS" title="Tests">⚠️</a></td>
     <td align="center"><a href="https://twitter.com/layershifter"><img src="https://avatars.githubusercontent.com/u/14183168?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Oleksandr Fediashov</b></sub></a><br /><a href="https://github.com/kentcdodds/rtl-css-js/commits?author=layershifter" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/ling1726"><img src="https://avatars.githubusercontent.com/u/20744592?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Lingfan Gao</b></sub></a><br /><a href="https://github.com/kentcdodds/rtl-css-js/commits?author=ling1726" title="Code">💻</a> <a href="https://github.com/kentcdodds/rtl-css-js/commits?author=ling1726" title="Tests">⚠️</a></td>
   </tr>
 </table>