Bump tensorflow from 1.0.0 to 1.15.2 in /requirements

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 1.0.0 to 1.15.2.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](tensorflow/tensorflow@v1.0.0...v1.15.2)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements/requirements.txt

@@ -8,4 +8,4 @@ keras==2.0.2
 scikit-learn==0.18.1
 pillow==4.0.0
 ipykernel==4.6.1
-tensorflow==1.0.0
+tensorflow==1.15.2