Bump tensorflow from 1.12.0 to 2.3.1

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 1.12.0 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/v1.12.0...v2.3.1)
Signed-off-by: Ndependabot[bot] <support@github.com>

requirements.txt

@@ -20,6 +20,6 @@ scipy==1.1.0
 six==1.11.0
 tensorboard==1.12.0
 tensorboardX==1.4
-tensorflow==1.12.0
+tensorflow==2.3.1
 termcolor==1.1.0
 Werkzeug==0.14.1