Bump keras from 2.2.2 to 2.2.4 (#422)

Bumps [keras](https://github.com/keras-team/keras) from 2.2.2 to 2.2.4.
- [Release notes](https://github.com/keras-team/keras/releases)
- [Commits](keras-team/keras@2.2.2...2.2.4)

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

setup.py

@@ -8,7 +8,7 @@
                       'torch==0.4.1',
                       'torchvision==0.2.1',
                       'numpy==1.14.5',
-                      'keras==2.2.2',
+                      'keras==2.2.4',
                       'scikit-learn==0.20.1',
                       'scikit-image==0.13.1',
                       'tqdm==4.25.0',