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] <support@github.com>

Author: dependabot[bot]

requirements.txt

@@ -3,7 +3,7 @@ Flask==1.1.1
 gunicorn==20.0.0
 json5==0.8.5
 numpy==1.17.3
-tensorflow==2.3.1
+tensorflow==2.4.0
 spacy==2.3.4