Bump lodash from 4.17.11 to 4.17.21 (#212)

Bumps [lodash](https://github.com/lodash/lodash) from 4.17.11 to 4.17.21.
- [Release notes](https://github.com/lodash/lodash/releases)
- [Commits](lodash/lodash@4.17.11...4.17.21)

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

package-lock.json

@@ -9,7 +9,7 @@
     "gulp": "^4.0.1",
     "gulp-connect": "^5.7.0",
     "harmonize": "^2.0.0",
-    "lodash": "^4.17.11",
+    "lodash": "^4.17.21",
     "marked": "^0.6.2",
     "metalsmith": "^2.3.0",
     "metalsmith-beautify": "^0.2.0",