Bump iso8601 from 0.1.12 to 0.1.13

Bumps [iso8601](https://github.com/micktwomey/pyiso8601) from 0.1.12 to 0.1.13.
- [Release notes](https://github.com/micktwomey/pyiso8601/releases)
- [Commits](micktwomey/pyiso8601@0.1.12...0.1.13)

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

requirements.txt

@@ -9,7 +9,7 @@ cornice-swagger==1.0.0
 dockerflow==2020.6.0
 hupper==1.10.2
 idna==2.10
-iso8601==0.1.12
+iso8601==0.1.13
 jsonpatch==1.26
 jsonpointer==2.0
 jsonschema==3.2.0