Update README.md

Author: haoda-li

README.md

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 # Mkdocs Plotly Plugin
 
-![PyPI](https://img.shields.io/pypi/v/mkdocs-plotly-plugin)
-![PyPI - Downloads](https://img.shields.io/pypi/dm/mkdocs-plotly-plugin)
-![PyPI - License](https://img.shields.io/pypi/l/mkdocs-plotly-plugin)
+![PyPI](https://img.shields.io/pypi/v/mkdocs-plotly-plugin?style=for-the-badge)
+![PyPI - Downloads](https://img.shields.io/pypi/dm/mkdocs-plotly-plugin?style=for-the-badge)
+![PyPI - License](https://img.shields.io/pypi/l/mkdocs-plotly-plugin?style=for-the-badge)
 
 [MkDocs](https://www.mkdocs.org/) plugin to create interactive charts from data using the declarative [plotly](https://plotly.com/javascript/)'s json syntax.