Update libgit2 submodule to master branch (#567)

alexcrichton · web-flow · commit 622b6eedb52a · 2020-06-03T10:10:28.000-05:00
Pulls in a libgit2/libgit2#5536 to fix rust-lang/cargo#8258
diff --git a/libgit2-sys/libgit2 b/libgit2-sys/libgit2
@@ -1 +1 @@
-Subproject commit 7d3c7057f0e774aecd6fc4ef8333e69e5c4873e0
+Subproject commit 86b85492b1bc8eeb9ff1af25b92877969f17833a
