Deploy git 2.20.1 to depot_tools on a bleeding edge

Bug: 887141
Change-Id: Ieaa53c18b01f6882f1b8f48c252ec1f9847f94fa
Reviewed-on: https://chromium-review.googlesource.com/c/1416491
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Robbie Iannucci <iannucci@chromium.org>
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>

bootstrap/win/manifest_bleeding_edge.txt

@@ -17,4 +17,4 @@ $VerifiedPlatform windows-386 windows-amd64
 infra/python/cpython/${platform} version:2.7.13.chromium7
 
 @Subdir git
-infra/git/windows-${arch} version:2.18.0.chromium16
+infra/git/windows-${arch} version:2.20.1.chromium16