docs: add Vultraz as a contributor (keystonejs#1637)

* docs: update CONTRIBUTING.md

* docs: update .all-contributorsrc

.all-contributorsrc

@@ -274,7 +274,8 @@
       "avatar_url": "https://avatars0.githubusercontent.com/u/3558659?v=4",
       "profile": "https://github.com/Vultraz",
       "contributions": [
-        "code"
+        "code",
+        "doc"
       ]
     }
   ],

CONTRIBUTING.md

@@ -173,7 +173,7 @@ Thanks goes to these wonderful people ([emoji key](https://allcontributors.org/d
     <td align="center"><a href="http://simonswiss.com"><img src="https://avatars1.githubusercontent.com/u/485747?v=4" width="100px;" alt="Simon Vrachliotis"/><br /><sub><b>Simon Vrachliotis</b></sub></a><br /><a href="#example-simonswiss" title="Examples">💡</a> <a href="#tutorial-simonswiss" title="Tutorials">✅</a> <a href="#video-simonswiss" title="Videos">📹</a></td>
   </tr>
   <tr>
-    <td align="center"><a href="https://github.com/Vultraz"><img src="https://avatars0.githubusercontent.com/u/3558659?v=4" width="100px;" alt="Charles Dang"/><br /><sub><b>Charles Dang</b></sub></a><br /><a href="https://github.com/keystonejs/keystone-5/commits?author=Vultraz" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/Vultraz"><img src="https://avatars0.githubusercontent.com/u/3558659?v=4" width="100px;" alt="Charles Dang"/><br /><sub><b>Charles Dang</b></sub></a><br /><a href="https://github.com/keystonejs/keystone-5/commits?author=Vultraz" title="Code">💻</a> <a href="https://github.com/keystonejs/keystone-5/commits?author=Vultraz" title="Documentation">📖</a></td>
   </tr>
 </table>