Bump tensorflow from 2.3.1 to 2.4.0

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 2.3.1 to 2.4.0.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](tensorflow/tensorflow@v2.3.1...v2.4.0)

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

Author: dependabot[bot]

requirements.txt

@@ -74,7 +74,7 @@ six==1.14.0
 tensorboard==2.1.1
 tensorboard-plugin-wit==1.6.0.post3
 tensorboardX==2.0
-tensorflow==2.3.1
+tensorflow==2.4.0
 tensorflow-estimator==2.1.0
 termcolor==1.1.0
 terminado==0.8.3