Bump tensorflow from 1.15.2 to 2.3.1

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 1.15.2 to 2.3.1.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](https://github.com/tensorflow/tensorflow/compare/v1.15.2...v2.3.1)

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

requirements.txt

@@ -1,7 +1,7 @@
 numpy==1.17.0
 opencv-python==4.1.0.25
 scipy==1.4.1
-tensorflow==1.15.2
+tensorflow==2.3.1
 colorama==0.4.3
 tqdm==4.47.0
 ffmpeg-python==0.2.0