docs: add mumenthalers as a contributor for code, and test (#466)

Author: allcontributors[bot]

.all-contributorsrc

@@ -370,6 +370,16 @@
         "code",
         "test"
       ]
+    },
+    {
+      "login": "mumenthalers",
+      "name": "S. Mumenthaler",
+      "avatar_url": "https://avatars.githubusercontent.com/u/3604424?v=4",
+      "profile": "https://github.com/mumenthalers",
+      "contributions": [
+        "code",
+        "test"
+      ]
     }
   ],
   "contributorsPerLine": 7,

README.md

@@ -256,6 +256,7 @@ Thanks goes to these people ([emoji key][emojis]):
       <td align="center" valign="top" width="14.28%"><a href="https://github.com/TrustNoOneElse"><img src="https://avatars.githubusercontent.com/u/25935352?v=4?s=100" width="100px;" alt="Florian Pabst"/><br /><sub><b>Florian Pabst</b></sub></a><br /><a href="https://github.com/testing-library/angular-testing-library/commits?author=TrustNoOneElse" title="Code">💻</a></td>
       <td align="center" valign="top" width="14.28%"><a href="https://rochesterparks.org"><img src="https://avatars.githubusercontent.com/u/9759954?v=4?s=100" width="100px;" alt="Mark Goho"/><br /><sub><b>Mark Goho</b></sub></a><br /><a href="#maintenance-markgoho" title="Maintenance">🚧</a> <a href="https://github.com/testing-library/angular-testing-library/commits?author=markgoho" title="Documentation">📖</a></td>
       <td align="center" valign="top" width="14.28%"><a href="http://jwbaart.dev"><img src="https://avatars.githubusercontent.com/u/10973990?v=4?s=100" width="100px;" alt="Jan-Willem Baart"/><br /><sub><b>Jan-Willem Baart</b></sub></a><br /><a href="https://github.com/testing-library/angular-testing-library/commits?author=jwbaart" title="Code">💻</a> <a href="https://github.com/testing-library/angular-testing-library/commits?author=jwbaart" title="Tests">⚠️</a></td>
+      <td align="center" valign="top" width="14.28%"><a href="https://github.com/mumenthalers"><img src="https://avatars.githubusercontent.com/u/3604424?v=4?s=100" width="100px;" alt="S. Mumenthaler"/><br /><sub><b>S. Mumenthaler</b></sub></a><br /><a href="https://github.com/testing-library/angular-testing-library/commits?author=mumenthalers" title="Code">💻</a> <a href="https://github.com/testing-library/angular-testing-library/commits?author=mumenthalers" title="Tests">⚠️</a></td>
     </tr>
   </tbody>
 </table>