Bump xmlschema from 3.3.1 to 3.4.2

Bumps [xmlschema](https://github.com/sissaschool/xmlschema) from 3.3.1 to 3.4.2.
- [Release notes](https://github.com/sissaschool/xmlschema/releases)
- [Changelog](https://github.com/sissaschool/xmlschema/blob/master/CHANGELOG.rst)
- [Commits](sissaschool/xmlschema@v3.3.1...v3.4.2)

---
updated-dependencies:
- dependency-name: xmlschema
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

requirements.txt

@@ -13,5 +13,5 @@ setuptools >= 41
 six
 #typing-extensions == 3.7.4.1; python_version != '2.7'
 tzlocal
-xmlschema == 3.3.1; python_version == '2.7'
+xmlschema == 3.4.2; python_version == '2.7'
 urlquick