Update badges
Replace by
Replace drone CI badge status by GitHub action CI badge status
`blockdiag` generate block-diagram image file from spec-text file.
-.. image:: https://drone.io/bitbucket.org/blockdiag/blockdiag/status.png
- :target: https://drone.io/bitbucket.org/blockdiag/blockdiag
- :alt: drone.io CI build status
+.. image:: https://github.com/blockdiag/blockdiag/actions/workflows/main.yml/badge.svg
+ :target: https://github.com/blockdiag/blockdiag/actions/workflows/main.yml
+ :alt: GitHub Action CI build status
-.. image:: https://pypip.in/v/blockdiag/badge.png
+.. image:: https://img.shields.io/pypi/v/blockdiag
:target: https://pypi.python.org/pypi/blockdiag/
:alt: Latest PyPI version
-.. image:: https://pypip.in/d/blockdiag/badge.png
+.. image:: https://img.shields.io/pypi/dm/blockdiag
:target: https://pypi.python.org/pypi/blockdiag/
:alt: Number of PyPI downloads
