docs: add michaelwestphal as a contributor for code, test (#239)

Author: allcontributors[bot]

Diff for: .all-contributorsrc

@@ -235,6 +235,16 @@
         "code",
         "bug"
       ]
+    },
+    {
+      "login": "michaelwestphal",
+      "name": "Michael Westphal",
+      "avatar_url": "https://avatars.githubusercontent.com/u/1829174?v=4",
+      "profile": "https://github.com/michaelwestphal",
+      "contributions": [
+        "code",
+        "test"
+      ]
     }
   ],
   "contributorsPerLine": 7,

Diff for: README.md

@@ -214,6 +214,7 @@ Thanks goes to these people ([emoji key][emojis]):
     <td align="center"><a href="https://github.com/amitmiran137"><img src="https://avatars.githubusercontent.com/u/47772523?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Amit Miran</b></sub></a><br /><a href="#infra-amitmiran137" title="Infrastructure (Hosting, Build-Tools, etc)">🚇</a></td>
     <td align="center"><a href="https://github.com/jwillebrands"><img src="https://avatars.githubusercontent.com/u/8925?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Jan-Willem Willebrands</b></sub></a><br /><a href="https://github.com/testing-library/angular-testing-library/commits?author=jwillebrands" title="Code">💻</a></td>
     <td align="center"><a href="https://www.sandroroth.com"><img src="https://avatars.githubusercontent.com/u/16229645?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Sandro</b></sub></a><br /><a href="https://github.com/testing-library/angular-testing-library/commits?author=rothsandro" title="Code">💻</a> <a href="https://github.com/testing-library/angular-testing-library/issues?q=author%3Arothsandro" title="Bug reports">🐛</a></td>
+    <td align="center"><a href="https://github.com/michaelwestphal"><img src="https://avatars.githubusercontent.com/u/1829174?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Michael Westphal</b></sub></a><br /><a href="https://github.com/testing-library/angular-testing-library/commits?author=michaelwestphal" title="Code">💻</a> <a href="https://github.com/testing-library/angular-testing-library/commits?author=michaelwestphal" title="Tests">⚠️</a></td>
   </tr>
 </table>