Bump lxml in /公开课/文档/年薪50W+的Python程序员如何写代码/code/Python/opencourse

Bumps [lxml](https://github.com/lxml/lxml) from 4.5.0 to 4.9.1.
- [Release notes](https://github.com/lxml/lxml/releases)
- [Changelog](https://github.com/lxml/lxml/blob/master/CHANGES.txt)
- [Commits](https://github.com/lxml/lxml/compare/lxml-4.5.0...lxml-4.9.1)

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

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

公开课/文档/年薪50W+的Python程序员如何写代码/code/Python/opencourse/requirements.txt

@@ -12,7 +12,7 @@ isort==4.3.21
 jedi==0.17.0
 lazy-object-proxy==1.4.3
 line-profiler==3.0.2
-lxml==4.5.0
+lxml==4.9.1
 mccabe==0.6.1
 memory-profiler==0.57.0
 numpy==1.18.3