Bump pyinstaller from 4.5.1 to 5.13.1 in /src/pyflask

Bumps [pyinstaller](https://github.com/pyinstaller/pyinstaller) from 4.5.1 to 5.13.1.
- [Release notes](https://github.com/pyinstaller/pyinstaller/releases)
- [Changelog](https://github.com/pyinstaller/pyinstaller/blob/develop/doc/CHANGES.rst)
- [Commits](pyinstaller/pyinstaller@v4.5.1...v5.13.1)

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

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

Author: dependabot[bot]

src/pyflask/requirements.txt

@@ -10,7 +10,7 @@ itsdangerous==2.0.1
 Jinja2==3.0.1
 jsonschema==3.2.0
 MarkupSafe==2.0.1
-pyinstaller==4.5.1
+pyinstaller==5.13.1
 pyinstaller-hooks-contrib==2021.3
 pyrsistent==0.18.0
 pytz==2021.1