Bump prismjs from 1.20.0 to 1.21.0

Bumps [prismjs](https://github.com/PrismJS/prism) from 1.20.0 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/v1.20.0...v1.21.0)

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

package-lock.json

@@ -7512,9 +7512,9 @@
       }
     },
     "prismjs": {
-      "version": "1.20.0",
-      "resolved": "https://registry.npmjs.org/prismjs/-/prismjs-1.20.0.tgz",
-      "integrity": "sha512-AEDjSrVNkynnw6A+B1DsFkd6AVdTnp+/WoUixFRULlCLZVRZlVQMVWio/16jv7G1FscUxQxOQhWwApgbnxr6kQ==",
+      "version": "1.21.0",
+      "resolved": "https://registry.npmjs.org/prismjs/-/prismjs-1.21.0.tgz",
+      "integrity": "sha512-uGdSIu1nk3kej2iZsLyDoJ7e9bnPzIgY0naW/HdknGj61zScaprVEVGHrPoXqI+M9sP0NDnTK2jpkvmldpuqDw==",
       "requires": {
         "clipboard": "^2.0.0"
       }

package.json

@@ -27,7 +27,7 @@
     "@postlight/mercury-parser": "^2.2.0",
     "axios": "^0.19.0",
     "babel-runtime": "^6.26.0",
-    "prismjs": "^1.20.0",
+    "prismjs": "^1.21.0",
     "vue": "^2.6.10",
     "vue-markdown": "^2.2.4",
     "vue-prism-editor": "^0.6.1",