Upgrade JGit to latest master revision
Upgrade JGit to latest master revision

This update includes the following commits:

271051ef0 - Replace "Rebase interactive" with "Interactive rebase"
5625f70d2 - [errorprone] Don't throw exception in finally
6ba8f37ab - [errorprone] Add parenthesis to clarify operator precedence
6a39da37f - GPG: implement more OpenPGP UserId matching formats

There is nothing specific that we need; this is just to keep up to
date with the latest head of the master branch.

Change-Id: If7b30c7d149ef04112b9379ad61ed7b540adaf43

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