Bump tensorflow from 1.15.0 to 1.15.2 in /src

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 1.15.0 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@v1.15.0...v1.15.2)

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

Author: dependabot[bot]

src/requirements.txt

@@ -25,7 +25,7 @@ regex==2017.4.5
 requests==2.21.0
 six==1.12.0
 tensorboard==1.13.1
-tensorflow==1.15.0
+tensorflow==1.15.2
 tensorflow-estimator==1.13.0
 termcolor==1.1.0
 tqdm==4.31.1