Bump tensorflow-gpu from 2.0.0 to 2.4.0

Bumps [tensorflow-gpu](https://github.com/tensorflow/tensorflow) from 2.0.0 to 2.4.0.
- [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/v2.0.0...v2.4.0)

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

requirements.txt

@@ -22,7 +22,7 @@ scipy==1.6.3
 six==1.12.0
 tensorboard==2.0.0
 tensorflow-estimator==2.0.0
-tensorflow-gpu==2.0.0
+tensorflow-gpu==2.4.0
 termcolor==1.1.0
 Werkzeug==0.16.0
 wrapt==1.11.2