fix: upgrade lodash from 4.17.15 to 4.17.21

Snyk has created this PR to upgrade lodash from 4.17.15 to 4.17.21.

See this package in npm:
https://www.npmjs.com/package/lodash

See this project in Snyk:
https://app.snyk.io/org/jswheeler/project/6e56448f-ed45-4265-9fd0-eddb0c6ab668?utm_source=github&utm_medium=referral&page=upgrade-pr

package.json

@@ -20,7 +20,7 @@
     "express": "^4.16.4",
     "express-session": "^1.17.0",
     "isomorphic-unfetch": "^3.0.0",
-    "lodash": "^4.17.15",
+    "lodash": "^4.17.21",
     "next": "^7.0.2",
     "prop-types": "^15.6.2",
     "react": "^16.5.2",