Upgrade merge script to run on python3

[asfimport]

It looks like the the parquet-java merge script is setup to run only on python2 which is EOL.  We should update it to run on python3 I plan to do this at least minimally without the Jira integration.

Reporter: Micah Kornfield / @emkornfield Assignee: Micah Kornfield / @emkornfield

PRs and other links:

• GitHub Pull Request #1373

_{Note: This issue was originally created as PARQUET-2495. Please see the migration documentation for further details.}