build(deps): bump moment from 2.19.1 to 2.21.0 in /docs

Bumps [moment](https://github.com/moment/moment) from 2.19.1 to 2.21.0.
- [Release notes](https://github.com/moment/moment/releases)
- [Changelog](https://github.com/moment/moment/blob/develop/CHANGELOG.md)
- [Commits](moment/moment@2.19.1...2.21.0)

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

Author: dependabot[bot]

docs/yarn.lock

@@ -2460,8 +2460,8 @@ mkdirp@^0.5.0, mkdirp@^0.5.1, mkdirp@~0.5.0, mkdirp@~0.5.1:
     minimist "0.0.8"
 
 moment@^2.11.2:
-  version "2.19.1"
-  resolved "https://registry.yarnpkg.com/moment/-/moment-2.19.1.tgz#56da1a2d1cbf01d38b7e1afc31c10bcfa1929167"
+  version "2.21.0"
+  resolved "https://registry.yarnpkg.com/moment/-/moment-2.21.0.tgz#2a114b51d2a6ec9e6d83cf803f838a878d8a023a"
 
 morgan@^1.8.1:
   version "1.9.1"