Update README.md

Author: haifeng-jin

README.md

@@ -5,8 +5,8 @@
 [![](https://github.com/keras-team/autokeras/workflows/Tests/badge.svg?branch=master)](https://github.com/keras-team/autokeras/actions?query=workflow%3ATests+branch%3Amaster)
 [![codecov](https://codecov.io/gh/keras-team/autokeras/branch/master/graph/badge.svg)](https://codecov.io/gh/keras-team/autokeras)
 [![PyPI version](https://badge.fury.io/py/autokeras.svg)](https://badge.fury.io/py/autokeras)
-![Python](https://img.shields.io/badge/python-v3.5.0+-success.svg)
-![Tensorflow](https://img.shields.io/badge/tensorflow-v2.3.0+-success.svg)
+![Python](https://img.shields.io/badge/python-v3.7.0+-success.svg)
+![Tensorflow](https://img.shields.io/badge/tensorflow-v2.5.0+-success.svg)
 [![contributions welcome](https://img.shields.io/badge/contributions-welcome-brightgreen.svg?style=flat)](https://github.com/keras-team/autokeras/issues)
 
 Official Website: [autokeras.com](https://autokeras.com)