Bump tensorflow from 2.0.0 to 2.3.1

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 2.0.0 to 2.3.1.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](tensorflow/tensorflow@v2.0.0...v2.3.1)

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

Author: dependabot[bot]

docs/requirements.txt

@@ -28,5 +28,5 @@ sphinxcontrib-serializinghtml==1.1.3
 urllib3==1.25.3
 sphinx-markdown-tables==0.0.9
 numpy==1.17.2
-tensorflow==2.0.0rc2
+tensorflow==2.4.0
 torch==1.2.0

requirements-dev.txt

@@ -36,7 +36,7 @@ sacremoses==0.0.35
 sentencepiece==0.1.83
 six==1.12.0
 tensorboard==2.0.0
-tensorflow==2.0.0
+tensorflow==2.4.0
 tensorflow-estimator==2.0.0
 termcolor==1.1.0
 torch==1.2.0