Update moment.js due to a security vulnerability

Versions of moment.js prior to 2.19.3 have a security vulnerability.
See CVE-2017-18214 for more details.

package-lock.json

@@ -1524,9 +1524,9 @@
       }
     },
     "moment": {
-      "version": "2.18.1",
-      "resolved": "https://registry.npmjs.org/moment/-/moment-2.18.1.tgz",
-      "integrity": "sha1-w2GT3Tzhwu7SrbfIAtu8d6gbHA8="
+      "version": "2.21.0",
+      "resolved": "https://registry.npmjs.org/moment/-/moment-2.21.0.tgz",
+      "integrity": "sha512-TCZ36BjURTeFTM/CwRcViQlfkMvL1/vFISuNLO5GkcVm1+QHfbSiNqZuWeMFjj1/3+uAjXswgRk30j1kkLYJBQ=="
     },
     "ms": {
       "version": "2.0.0",

package.json

@@ -15,7 +15,7 @@
     "humanize-duration": "^3.10.0",
     "knex": "^0.14.2",
     "mime": "^1.3.4",
-    "moment": "^2.17.1",
+    "moment": "^2.21.0",
     "public-ip": "^2.0.1",
     "sqlite3": "^3.1.13",
     "transliteration": "^1.6.2",