Bump tensorflow from 2.7.0 to 2.8.0

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 2.7.0 to 2.8.0.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](tensorflow/tensorflow@v2.7.0...v2.8.0)

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

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

Author: dependabot[bot]

requirements.txt

@@ -39,10 +39,10 @@ requests-oauthlib==1.3.0
 rsa==4.7
 scipy==1.4.1
 six==1.15.0
-tensorboard==2.7.0
+tensorboard==2.8.0
 tensorboard-plugin-wit==1.6.0.post3
-tensorflow==2.7.0
-tensorflow-estimator==2.7.0
+tensorflow==2.8.0
+tensorflow-estimator==2.8.0
 tensorflow-io-gcs-filesystem==0.23.1
 termcolor==1.1.0
 toml==0.10.1