Bump prismjs from 1.20.0 to 1.21.0 in /example

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](PrismJS/prism@v1.20.0...v1.21.0)

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

Author: dependabot[bot]

example/yarn.lock

@@ -4347,9 +4347,9 @@ prepend-http@^1.0.0:
   integrity sha1-1PRWKwzjaW5BrFLQ4ALlemNdxtw=
 
 prismjs@^1.20.0:
-  version "1.20.0"
-  resolved "https://registry.yarnpkg.com/prismjs/-/prismjs-1.20.0.tgz#9b685fc480a3514ee7198eac6a3bf5024319ff03"
-  integrity sha512-AEDjSrVNkynnw6A+B1DsFkd6AVdTnp+/WoUixFRULlCLZVRZlVQMVWio/16jv7G1FscUxQxOQhWwApgbnxr6kQ==
+  version "1.21.0"
+  resolved "https://registry.yarnpkg.com/prismjs/-/prismjs-1.21.0.tgz#36c086ec36b45319ec4218ee164c110f9fc015a3"
+  integrity sha512-uGdSIu1nk3kej2iZsLyDoJ7e9bnPzIgY0naW/HdknGj61zScaprVEVGHrPoXqI+M9sP0NDnTK2jpkvmldpuqDw==
   optionalDependencies:
     clipboard "^2.0.0"