v0.21.6

Version 0.21.6

Commits

• [46d83aa] Fix MPRester import in core client (#567)
• [32c45ba] Update README.md
• [64c229b] Fix electrode test
• [6785935] Update reqs
• [77f4af7] Bump maggma from 0.40.0 to 0.44.1 (#551)
• [e08de40] Bump emmet-core from 0.21.19 to 0.21.20 (#540)
• [d1a79a5] Add back windows testing