Bump jsonpatch from 1.26 to 1.28

Bumps [jsonpatch](https://github.com/stefankoegl/python-json-patch) from 1.26 to 1.28.
- [Release notes](https://github.com/stefankoegl/python-json-patch/releases)
- [Commits](stefankoegl/python-json-patch@v1.26...v1.28)

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

requirements.txt

@@ -12,7 +12,7 @@ dockerflow==2020.6.0
 hupper==1.10.2
 idna==2.10
 iso8601==0.1.12
-jsonpatch==1.26
+jsonpatch==1.28
 jsonpointer==2.0
 jsonschema==3.2.0
 kinto==14.1.1