Binder doesn't work due to old branch names

[paulmaunders]

I used generate_badge() to add a binder badge to my repo, however when clicking it binder gave the following error:

Could not resolve ref for gh:paulmaunders/coronavirus-graphs/master. Double check your URL. GitHub recently changed default branches from "master"to "main". Did you mean the "main" branch?

Updating the badge link to main helped, but then I encountered another error:

Resolving github.com (github.com)... 140.82.114.4
Connecting to github.com (github.com)|140.82.114.4|:443... connected.
HTTP request sent, awaiting response... 404 Not Found
2020-12-31 17:43:32 ERROR 404: Not Found.

So it looks like the references to master in the DockerFile need updating too.