Update lxml requirement from ~=4.9.4 to ~=5.1.0 (#39)

Updates the requirements on [lxml](https://github.com/lxml/lxml) to permit the latest version.
- [Release notes](https://github.com/lxml/lxml/releases)
- [Changelog](https://github.com/lxml/lxml/blob/master/CHANGES.txt)
- [Commits](lxml/lxml@lxml-4.9.4...lxml-5.1.0)

---
updated-dependencies:
- dependency-name: lxml
  dependency-type: direct:production
...

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requirements.txt

@@ -1,2 +1,2 @@
 compal>=0.4.0
-lxml~=4.9.4
+lxml~=5.1.0