build(deps): bump prismjs from 1.15.0 to 1.21.0 in /web

Bumps [prismjs](https://github.com/PrismJS/prism) from 1.15.0 to 1.21.0.
- [Release notes](https://github.com/PrismJS/prism/releases)
- [Changelog](https://github.com/PrismJS/prism/blob/master/CHANGELOG.md)
- [Commits](https://github.com/PrismJS/prism/compare/v1.15.0...v1.21.0)

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

web/package.json

@@ -5,7 +5,7 @@
   "proxy": "http://127.0.0.1:8080",
   "dependencies": {
     "moment": "2.24.0",
-    "prismjs": "1.15.0",
+    "prismjs": "1.21.0",
     "react": "16.8.4",
     "react-clipboard.js": "2.0.7",
     "react-datepicker": "2.2.0",