Update JGit to 5.1.15.202012011955-r

This version fixes a bug occurring when processing a fetch request and
running gc concurrently.

Bug: https://bugs.eclipse.org/bugs/show_bug.cgi?id=569349
Change-Id: I605749727d39822683371b98d996f5afdf1604e9
diff --git a/lib/jgit/jgit.bzl b/lib/jgit/jgit.bzl
index 841b13e..eafb37b 100644
--- a/lib/jgit/jgit.bzl
+++ b/lib/jgit/jgit.bzl
@@ -1,6 +1,6 @@
 load("//tools/bzl:maven_jar.bzl", "MAVEN_CENTRAL", "maven_jar")
 
-_JGIT_VERS = "5.1.14.202011251942-r"
+_JGIT_VERS = "5.1.15.202012011955-r"
 
 _DOC_VERS = _JGIT_VERS  # Set to _JGIT_VERS unless using a snapshot
 
@@ -40,28 +40,28 @@
         name = "jgit-lib",
         artifact = "org.eclipse.jgit:org.eclipse.jgit:" + _JGIT_VERS,
         repository = _JGIT_REPO,
-        sha1 = "f962f10e9aac2c476eac02e6d37cf8ee9a101958",
-        src_sha1 = "afa2ff384db5b4a3dc75b0ef2f127d5ef474d635",
+        sha1 = "ca4a5fbd38cfad3ad386b46464b0e753eca3baea",
+        src_sha1 = "39a4180b70ac3024d68ee9781198e88abf567ccf",
         unsign = True,
     )
     maven_jar(
         name = "jgit-servlet",
         artifact = "org.eclipse.jgit:org.eclipse.jgit.http.server:" + _JGIT_VERS,
         repository = _JGIT_REPO,
-        sha1 = "b7c6e973495c75f2de8f837fac213c6b1d9a9860",
+        sha1 = "698fa84e35787eab380efadc2df52706dbac5268",
         unsign = True,
     )
     maven_jar(
         name = "jgit-archive",
         artifact = "org.eclipse.jgit:org.eclipse.jgit.archive:" + _JGIT_VERS,
         repository = _JGIT_REPO,
-        sha1 = "4331d91515347e416d914a90299f6d6070599efc",
+        sha1 = "27c731c41c8cb45e6bccdaac14311bda1d724437",
     )
     maven_jar(
         name = "jgit-junit",
         artifact = "org.eclipse.jgit:org.eclipse.jgit.junit:" + _JGIT_VERS,
         repository = _JGIT_REPO,
-        sha1 = "5fd2a105454dd8b4834a37667ec12111d691167a",
+        sha1 = "6f961edbfecf5928c87d46b08acf2e1625a53089",
         unsign = True,
     )