Bump jsonschema from 2.6.0 to 3.0.0

Bumps [jsonschema](https://github.com/Julian/jsonschema) from 2.6.0 to 3.0.0.
- [Release notes](https://github.com/Julian/jsonschema/releases)
- [Changelog](https://github.com/Julian/jsonschema/blob/master/CHANGELOG.rst)
- [Commits](python-jsonschema/jsonschema@v2.6.0...v3.0.0)

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

requirements.txt

@@ -12,7 +12,7 @@ idna==2.8
 iso8601==0.1.12
 jsonpatch==1.23
 jsonpointer==2.0
-jsonschema==2.6.0
+jsonschema==3.0.0
 kinto==13.0.1
 logging-color-formatter==1.0.2
 PasteDeploy==2.0.1