Update dependency lodash to v4.17.21

Author: mend-for-github-com[bot]

package-lock.json

@@ -20,7 +20,7 @@
     "semver": "5.7.1",
     "to": "0.2.9",
     "url": "0.11.0",
-    "lodash": "4.17.15",
+    "lodash": "4.17.21",
     "marked": "0.3.19"
   },
   "devDependencies": {