Bump regex from 2020.11.13 to 2021.4.4

Bumps [regex](https://bitbucket.org/mrabarnett/mrab-regex) from 2020.11.13 to 2021.4.4.
- [Commits](https://bitbucket.org/mrabarnett/mrab-regex/commits)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

dev-requirements.txt

@@ -28,7 +28,7 @@ pytest-clarity==0.3.0a0
 pytest-cov==2.10.1
 pytest-sugar==0.9.4
 pytest==6.2.1
-regex==2020.11.13
+regex==2021.4.4
 snowballstemmer==2.1.0
 termcolor==1.1.0
 toml==0.10.2; python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2'