Bump bleach from 3.1.0 to 3.3.0 in /getting-started

Bumps [bleach](https://github.com/mozilla/bleach) from 3.1.0 to 3.3.0.
- [Release notes](https://github.com/mozilla/bleach/releases)
- [Changelog](https://github.com/mozilla/bleach/blob/master/CHANGES)
- [Commits](mozilla/bleach@v3.1.0...v3.3.0)

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

getting-started/requirements.txt

@@ -2,7 +2,7 @@ altair==3.2.0
 appnope==0.1.0
 attrs==19.3.0
 backcall==0.1.0
-bleach==3.1.0
+bleach==3.3.0
 certifi
 chardet==3.0.4
 decorator==4.4.1