Bump tensorflow from 1.3.0 to 1.15.2

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 1.3.0 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@v1.3.0...v1.15.2)

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

Author: dependabot[bot]

requirements.txt

@@ -1,7 +1,7 @@
 Flask==1.1.0
 gunicorn==19.6.0
 scipy==0.18.1
-tensorflow==1.4.0
+tensorflow==1.15.2
 numpy==1.12.1
 Tkinter
 tqdm==4.11.2

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