Bump tensorflow from 2.8.0 to 2.8.1 in /examples/wmt

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 2.8.0 to 2.8.1.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](tensorflow/tensorflow@v2.8.0...v2.8.1)

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

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

examples/wmt/requirements.txt

@@ -9,6 +9,6 @@ numpy==1.21.4
 optax==0.1.0
 sentencepiece==0.1.96
 six==1.15.0
-tensorflow==2.8.0
+tensorflow==2.8.1
 tensorflow-datasets==4.4.0
 tensorflow-text==2.8.1