Upgrade JGit to v5.6.1.202002131546-r-19-ga79c5b1f1
Upgrade JGit to v5.6.1.202002131546-r-19-ga79c5b1f1

This updates JGit to the latest head of the stable-5.6 branch
and introduces the following commits:

a79c5b1f1 - Remove double blank from sentence start
3851023e0 - Bump Bazel version to 3.0.0
2640d38f1 - FS.runInShell(): handle quoted filters and hooksPath containing blanks
24f82b533 - Handle non-normalized index also for executable files

None of these are specifically needed by Gerrit; this update is
only to keep up to date with the latest revision.

Change-Id: I4e12c697284f526eb14f47b784c6f7686ad05434

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