Upgrade JGit to v5.6.0.201912041214-rc1

Include the following changes:

a7e454bc5 - JGit v5.6.0.201912041214-rc1
4ea42bc81 - Prepare 5.6.0-SNAPSHOT builds
6c9aa82f7 - JGit v5.6.0.201911271000-m3
5897bc430 - ReceivePack: Open visibility for some methods
533a81db9 - JGit pgm: Format blame output to match canonical git
59f9d206c - Make blame work correctly on merge conflicts
7554bdfad - Bazel: Use java_plugin and java_binary from @rules_java in jmh.bzl
2c5ed560c - Bazel: Add missing newlines at end of BUILD files
8041b71c7 - Upgrade maven-enforcer-plugin to 3.0.0-M3
ffb979bef - Add missing license header to ReftableDatabase
3e01123a5 - Add missing license header to UploadPackRefSortingForReachabilityTest
3d4c95293 - [spotbugs] Fix potential NPE in FSTest
74487ffa1 - Remove unused import in CreateFileSnapshotBenchmark
9cb8e2f31 - RepositoryCache: don't require HEAD in git repositories
e0744891f - FileRepository: cleanup refs outside refs/ on reftable conversion
fd51cd159 - Update Orbit to S20191118194249 for 2019-12 M3
75038afc8 - Silence API error for new method in ReachabilityChecker
f2ccc4213 - UploadPackTest: Fix unused parameter in checkUnadvertisedIfUnallowed
f5f5c80bf - BitmappedReachabilityChecker: Use only one bitmap for the whole check
989a927a5 - checkNotAdvertisedWants: Be lazy converting Ref to RevCommit
a0204a472 - ReachabilityChecker: Receive a Stream instead of a Collection
2ff0c0aba - UploadPack: Prioritize references for non-advertised wants checks
fa1566f40 - ReceivePack: Fix name hiding of 'atomic' member
e9c21fca5 - ReceivePack: Remove unnecessarily nested else-clause
f8e60ce1c - Simplify comparator code
8fcba48b7 - Fix typo in Javadoc
0356613f4 - pgm: add write stats to BenchmarkReftable
a8f4bf6ab - pgm: add command to convert repo to reftable
38586d54d - file: implement FileReftableDatabase
7b73d5eec - Fix Maven missing version warning
7ab7ec00c - Use Java 8 source and target in Maven
a6bdcace3 - ReceivePack: Reduce visibility of methods
830e7bf67 - Suppress API error raised for constant added in 345e2648
cb85f7be8 - TopoSortGenerator: simplify first-parent handling
1daf6f13a - RewriteGenerator: avoid adding null parent
345e2648d - DiffFormatter: support core.quotePath = false
a227dc3ba - IndexDiff/SubmoduleWalk: make the RepositoryBuilder configurable
7a3b93cbe - IndexDiff/SubmoduleWalk: handle submodule.<name>.ignore correctly
63fba337b - Run Eclipse formatter on BatchRefUpdateTest
74bfec411 - Move KetchSystem.delay to FileUtils.

Change-Id: I82d728f4583e7c6b85643ebdc008e4a161c2e781
diff --git a/modules/jgit b/modules/jgit
index 63fc697..a7e454b 160000
--- a/modules/jgit
+++ b/modules/jgit
@@ -1 +1 @@
-Subproject commit 63fc6970cc51b712608d93e7cba0b85bb559ac52
+Subproject commit a7e454bc51d359c2d46b19fd559f770cad8fd7d4