Bump iso8601 from 2.0.0 to 2.1.0

Bumps [iso8601](https://github.com/micktwomey/pyiso8601) from 2.0.0 to 2.1.0.
- [Release notes](https://github.com/micktwomey/pyiso8601/releases)
- [Changelog](https://github.com/micktwomey/pyiso8601/blob/main/CHANGELOG.md)
- [Commits](micktwomey/pyiso8601@2.0.0...2.1.0)

---
updated-dependencies:
- dependency-name: iso8601
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

requirements.txt

@@ -1,7 +1,7 @@
 colander==2.0
 cornice==6.0.1
 hupper==1.12
-iso8601==2.0.0
+iso8601==2.1.0
 PasteDeploy==3.0.1
 plaster==1.1.2
 plaster-pastedeploy==1.0.1