Bump waitress from 1.4.3 to 2.1.1 in /examples/falcon_mongoengine

Bumps [waitress](https://github.com/Pylons/waitress) from 1.4.3 to 2.1.1.
- [Release notes](https://github.com/Pylons/waitress/releases)
- [Changelog](https://github.com/Pylons/waitress/blob/master/CHANGES.txt)
- [Commits](Pylons/waitress@v1.4.3...v2.1.1)

---
updated-dependencies:
- dependency-name: waitress
  dependency-type: direct:production
...

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

Author: dependabot[bot]

examples/falcon_mongoengine/requirements.txt

@@ -1,6 +1,6 @@
 falcon==2.0.0
 mongoengine==0.17.0
 graphene-mongo
-waitress==1.4.3
+waitress==2.1.1
 pytest==4.6.3
 mongomock==3.16.0