Fixed movie dataset columns in examples and docs

[ANich]

Hey, awesome library!

I updated a few of the broken examples and docs mentioned here #2213 (comment) (that use the movie dataset).

I wasn't able to build the docs locally so I looked them over in a jupyter notebook using altair=4.1.0 and vega_datasets=0.8.0 and they looked fine.

I started looking at altair/examples/multiple_interactions.py as well but I ran into this upstream issue vega/vega-lite#4870 so I left it alone

[ANich]

If someone else could check with built docs that'd be great! Here's my problem:

After running pip install -r requirements in doc/ I got the following error:
Could not import extension altair.sphinxext.schematable (exception: No module named 'recommonmark')

So I ran pip install recommonmark, now make html gives me the following error:
Handler <function main at 0x7fa1f33dfae8> for event 'builder-inited' threw an exception

[ANich]

I was able to build the docs, I just had to follow some instructions in CONTRIBUTING and RELEASING. I opened #2306 to make this a little easier for future contributors.

(Btw this also addresses #2291 except altair/examples/multiple_interactions.py because of the upstream issue 🙂 )

Here are some screenshots:

[ANich]

Not relevant anymore