ENH: Change to CDN for base url

[eitanlees]

resolves #41

[eitanlees]

vega_datasets/__init__.py:5:1: E402 module level import not at top of file

So the build is failing flake8 because I moved SOURCE_TAG to the top of the __init__.py file. The reason I did this is so it can be referenced in core.py

What do you recomend?

We could change the test to ignore E402, or do something else to access the SOURCE_TAG. Maybe even more it into core.py?

[eitanlees]

I went ahead and moved SOURCE_TAG into core.py.

I also modified generate_datasets_json.py such that it updates the correct file.

I think this should be working as expected now.

[jakevdp]

Looks good! To populate the new URLs within the package, run python tools/generate_datasets_json.py

Edit: nevermind, this is not necessary.

But it would be useful to run this just to make sure it works, since the tools are not covered by tests!

[eitanlees]

yes, I checked that it worked locally

[jakevdp]

Thanks!