Bump hyperkitty from 1.3.6 to 1.3.7 in /web (#590)

Bumps [hyperkitty](https://gitlab.com/mailman/hyperkitty) from 1.3.6 to 1.3.7.
- [Release notes](https://gitlab.com/mailman/hyperkitty/tags)
- [Commits](https://gitlab.com/mailman/hyperkitty/compare/v1.3.6...1.3.7)

---
updated-dependencies:
- dependency-name: hyperkitty
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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web/requirements.txt

@@ -1,4 +1,4 @@
 mailmanclient==3.3.4
 postorius==1.3.7
-hyperkitty==1.3.6
+hyperkitty==1.3.7
 django-mailman3==1.3.8