Upgrade for compatibility with Datasette 1.0

[simonw]

This plugin is currently broken in the Datasette 1.0 alphas because the table JSON has changed.

[simonw]

I ran this in my local development environment to upgrade to 1.0a5:

pip install --pre datasette -U

tests/test_docs.py ................                                                [ 21%]
tests/test_graphql.py .....FFFFFFFFFFFFFFF.FFFFFFF...FF.FFFF.FF......FFF.          [ 91%]
tests/test_plugin_hook.py .                                                        [ 93%]
tests/test_schema_caching.py .                                                     [ 94%]
tests/test_schema_for_database.py F                                                [ 95%]
tests/test_template_tag.py FF                                                      [ 98%]
tests/test_utils.py .                                                              [100%]

[simonw]

I'm going to push an alpha release from the new datasette-1-compat branch. I'll make it 3.0a0.