Version: 0.7.2, update docs and dependencies to boardame.io v50

[on3iro]

Hi @delucis ,

I just recently discovered this awesome plugin, but soon realized, that its build and docs have not yet been upgraded to the latest boardgame.io version.
Therefore I tried to incorporate the necessary changes. I hope I did not forget anything.
Just let me know if this works for you or if I should change anything.
Oh and if you don't intend to update this to bgio v50, we should probably at least note this somewhere in the docs.

On a side note: I am not sure, yet, but I assume there are also a few outdated boardgame.io docs, that do not match the new v50 types. I also noticed that the boardgame.io documentation seems to take really long to load in the last couple of days.