Bump tensorflow from 1.13.1 to 1.15.0 in /utils/tfrecords (#967)

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 1.13.1 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@v1.13.1...v1.15.0)

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

Author: dependabot[bot]

utils/tfrecords/requirements.txt

@@ -1,3 +1,3 @@
 argparse==1.1
-tensorflow==1.13.1
+tensorflow==1.15.0
 pathlib==1.0.1