Upgrade to Pyarrow 1.0

[devin-petersohn]

In #1377 we require pyarrow<0.17, but since Pyarrow 1.0 released, we should update to new stable API.

[itamarst]

Gandiva appears to be no longer part of the default pyarrow wheel (apache/arrow#7334).

There is an open issue to package it separately: https://issues.apache.org/jira/browse/ARROW-8518

[devin-petersohn]

Thanks @itamarst, this will be an issue in updating. Unfortunately that issue is slated for resolution in version 2. We probably will have to make the gandiva import conditional.