Update URLs and field names to match the new vega weather datasets

[joelostblom]

This fixes the broken weather sections in the docs mentioned in #2213. I upated based on my understanding of altair-viz/vega_datasets#40.

[joelostblom]

All test failures are related to me using the new name for the seattle data set from altair-viz/vega_datasets#40, and should be fixed once that is merged.

[jakevdp]

Thanks for this.

What needs to happen to fix this issue:

• a new minor release of vega-datasets 1.X that pins the old URLs, so that it can work with older Altair versions
• a new micro release of Altair with accompanying doc build with the older vega-datasets path
• a new minor release of Altair that makes all the required updates to work with vega-datasets 2.X

I've not done that yet, because it's a ~half day of work to get right, and I've not had an open half day in half a year.

[jakevdp]

I should say: thanks for the contribution. I really appreciate it. But we can't merge changes like this until 1 & 2 are done.

[joelostblom]

Thank you for responding so quickly! I understand that you are super busy and I didn't want to stress, more just checking in if I could do something helpful for moving this forward. But it sounds like most things you mentioned are release related, which sounds a bit tricky to help with.

[mattijn]

fixed by #3859