Bump tensorflow from 1.13.0rc2 to 1.15.0

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 1.13.0rc2 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@v1.13.0-rc2...v1.15.0)

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

Author: dependabot[bot]

requirements.txt

@@ -1,6 +1,6 @@
 h5py==2.8.0
 Keras==2.2.4
-tensorflow==1.13.0rc2
+tensorflow==1.15.0
 dlib==19.16.0
 opencv_python==3.4.3.18
 imutils==0.5.1