How to make Flint work with Spark 3.0

Hi n00b question: given how awesome and popular Flint has been, I'm really interested in making it work with Spark 3.0.

So I went ahead and tried the changes in https://github.com/twosigma/flint/pull/82/files which made Flint build successfully with Spark 3.0-preview2, but now some tests are failing (see
[flint-spark-3.0.0-build.log](https://github.com/twosigma/flint/files/4667907/flint-spark-3.0.0-build.log) ), and I'm not completely sure how to fix the test failures or how much work it might take to fix them.

Any idea how to resolve the test failures? Thanks in advance!