⬆️ Bump keras from 2.2.4 to 2.4.0

Bumps [keras](https://github.com/keras-team/keras) from 2.2.4 to 2.4.0.
- [Release notes](https://github.com/keras-team/keras/releases)
- [Commits](keras-team/keras@2.2.4...2.4.0)

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

setup.py

@@ -34,7 +34,7 @@
         'tensorflow>=1.12.0',
         'Flask>=1.0.2',
         'waitress>=1.1.0',
-        'keras==2.2.4',
+        'keras==2.4.0',
         'PTable>=0.9.2',
         'spacy>=2.0.11, <=2.0.13',
         'gensim>=3.4.0',