Bump keras from 2.2.5 to 2.3.0 (#963)

Bumps [keras](https://github.com/keras-team/keras) from 2.2.5 to 2.3.0.
- [Release notes](https://github.com/keras-team/keras/releases)
- [Commits](https://github.com/keras-team/keras/compare/2.2.5...2.3.0)

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

extra-nn-requirements.txt

@@ -1,2 +1,2 @@
-keras==2.2.5
+keras==2.3.0
 tensorflow==1.14.0