Bump tensorflow in /financial_time_series/tensorflow_model

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 2.5.3 to 2.7.2.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](tensorflow/tensorflow@v2.5.3...v2.7.2)

---
updated-dependencies:
- dependency-name: tensorflow
  dependency-type: direct:production
...

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

Author: dependabot[bot]

financial_time_series/tensorflow_model/requirements.txt

@@ -2,4 +2,4 @@ google-cloud-storage==1.17.0
 google-cloud-bigquery==1.6.0
 pandas==0.23.4
 numpy==1.16.0
-tensorflow==2.5.3
+tensorflow==2.7.2