Bump showdown from 1.8.6 to 1.9.0

Bumps [showdown](https://github.com/showdownjs/showdown) from 1.8.6 to 1.9.0.
- [Release notes](https://github.com/showdownjs/showdown/releases)
- [Changelog](https://github.com/showdownjs/showdown/blob/master/CHANGELOG.md)
- [Commits](https://github.com/showdownjs/showdown/compare/1.8.6...1.9.0)
Signed-off-by: dependabot[bot] <support@dependabot.com>

yarn.lock

@@ -7695,9 +7695,9 @@ shelljs@^0.7.5:
     rechoir "^0.6.2"
 
 showdown@^1.6.4:
-  version "1.8.6"
-  resolved "https://registry.yarnpkg.com/showdown/-/showdown-1.8.6.tgz#91ea4ee3b7a5448aaca6820a4e27e690c6ad771c"
-  integrity sha1-kepO47elRIqspoIKTifmkMatdxw=
+  version "1.9.0"
+  resolved "https://registry.yarnpkg.com/showdown/-/showdown-1.9.0.tgz#d49d2a0b6db21b7c2e96ef855f7b3b2a28ef46f4"
+  integrity sha512-x7xDCRIaOlicbC57nMhGfKamu+ghwsdVkHMttyn+DelwzuHOx4OHCVL/UW/2QOLH7BxfCcCCVVUix3boKXJKXQ==
   dependencies:
     yargs "^10.0.3"