Bump lodash from 4.17.20 to 4.17.21 in /samples/react-custom-links

Bumps [lodash](https://github.com/lodash/lodash) from 4.17.20 to 4.17.21.
- [Release notes](https://github.com/lodash/lodash/releases)
- [Commits](https://github.com/lodash/lodash/compare/4.17.20...4.17.21)

---
updated-dependencies:
- dependency-name: lodash
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

samples/react-custom-links/package-lock.json

@@ -18871,9 +18871,9 @@
       }
     },
     "lodash": {
-      "version": "4.17.20",
-      "resolved": "https://registry.npmjs.org/lodash/-/lodash-4.17.20.tgz",
-      "integrity": "sha512-PlhdFcillOINfeV7Ni6oF1TAEayyZBoZ8bcshTHqOYJYlrqzRK5hagpagky5o4HfCzzd1TRkXPMFq6cKk9rGmA=="
+      "version": "4.17.21",
+      "resolved": "https://registry.npmjs.org/lodash/-/lodash-4.17.21.tgz",
+      "integrity": "sha512-v2kDEe57lecTulaDIuNTPy3Ry4gLGJ6Z1O3vE1krgXZNrsQ+LFTGHVxVjcXPs17LhbZVGedAJv8XZ1tvj5FvSg=="
     },
     "lodash._basecopy": {
       "version": "3.0.1",

samples/react-custom-links/package.json

@@ -44,7 +44,7 @@
     "ajv": "~5.2.2",
     "gulp": "~4.0.2",
     "gulp-sequence": "1.0.0",
-    "lodash": "^4.17.15",
+    "lodash": "^4.17.21",
     "spfx-uifabric-themes": "^0.8.0",
     "typescript": "~3.7.x"
   }