Update tensorflow requirement

Updates the requirements on [tensorflow](https://github.com/tensorflow/tensorflow) to permit the latest version.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](tensorflow/tensorflow@v2.0.0...v2.8.0)

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

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

Author: dependabot[bot]

setup.py

@@ -41,7 +41,7 @@ def readme():
           'scikit-image>=0.14.2, !=0.17.1, <0.20',  # https://github.com/SeldonIO/alibi/issues/215
           'requests>=2.21.0, <3.0.0',
           'Pillow>=5.4.1, <10.0',
-          'tensorflow>=2.0.0, !=2.6.0, !=2.6.1, <2.8.0',  # https://github.com/SeldonIO/alibi-detect/issues/375
+          'tensorflow>=2.0.0, !=2.6.0, !=2.6.1, <2.9.0',  # https://github.com/SeldonIO/alibi-detect/issues/375
           'attrs>=19.2.0, <22.0.0',
           'scipy>=1.1.0, <2.0.0',
           'matplotlib>=3.0.0, <4.0.0',