[Java] Java compilation failures on master

[asfimport]

Two Flight-related Java patches were merged today and we have compilation failures on master now:

https://travis-ci.org/apache/arrow/jobs/551015006#L956

Reporter: Wes McKinney / @wesm
Assignee: Micah Kornfield / @emkornfield

PRs and other links:

• GitHub Pull Request #4713

_{Note: This issue was originally created as ARROW-5750. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 4713
#4713