Bump tensorflow from 1.4.0 to 1.15.0

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 1.4.0 to 1.15.0.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](tensorflow/tensorflow@v1.4.0...v1.15.0)

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

setup.py

@@ -28,7 +28,7 @@
                     'wrangle',
                     'numpy',
                     'pandas',
-                    'tensorflow==1.4.0',
+                    'tensorflow==1.15.0',
                     'keras==2.3.0',
                     'astetik',
                     'sklearn',