build(deps): bump opencv-python from 3.1.0.0 to 3.4.7.28

Bumps [opencv-python](https://github.com/skvark/opencv-python) from 3.1.0.0 to 3.4.7.28.
- [Release notes](https://github.com/skvark/opencv-python/releases)
- [Commits](https://github.com/skvark/opencv-python/commits)

---
updated-dependencies:
- dependency-name: opencv-python
  dependency-type: direct:production
...

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

requirements.txt

@@ -8,7 +8,7 @@ pyzmq==18.1.0
 regex==2019.6.8
 Pillow==6.2.2
 pip==20.1
-opencv-python==3.1.0.0
+opencv-python==3.4.7.28
 opt-einsum==3.1.0
 packaging==19.2
 pandas==0.17.0