[Security] Bump waitress from 1.4.2 to 1.4.3

Bumps [waitress](https://github.com/Pylons/waitress) from 1.4.2 to 1.4.3. **This update includes a security fix.**
- [Release notes](https://github.com/Pylons/waitress/releases)
- [Changelog](https://github.com/Pylons/waitress/blob/master/CHANGES.txt)
- [Commits](Pylons/waitress@v1.4.2...v1.4.3)

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

requirements.txt

@@ -33,7 +33,7 @@ translationstring==1.3
 ujson==2.0.3
 urllib3==1.24.2
 venusian==3.0.0
-waitress==1.4.2
+waitress==1.4.3
 WebOb==1.8.6
 zope.deprecation==4.4.0
 zope.interface==5.1.0