Bump lodash from 4.17.20 to 4.17.21

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

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

Author: dependabot[bot]

package-lock.json

@@ -28,7 +28,7 @@
     "acorn": ">=5.7.4",
     "bulma": "^0.9.0",
     "html-minifier": "^4.0.0",
-    "lodash": "^4.17.19",
+    "lodash": "^4.17.21",
     "node-sass": "^4.14.0",
     "purgecss": "^2.3.0"
   },