Update windows git to 2.17.1

This is for security updates related to
CVE 2018-11235
CVE 2018-11234
https://public-inbox.org/git/xmqqy3g2flb6.fsf@gitster-ct.c.googlers.com/

Bug: 847597
Change-Id: I3b2d6b7bf9fe2d93bdc375903357f07f4fff8573
Reviewed-on: https://chromium-review.googlesource.com/1077307
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Aaron Gable <agable@chromium.org>

bootstrap/win/manifest.txt

@@ -17,4 +17,4 @@ $VerifiedPlatform windows-386 windows-amd64
 infra/python/cpython/windows-386 version:2.7.6
 
 @Subdir git
-infra/git/windows-${arch} version:2.17.0.chromium12
+infra/git/windows-${arch} version:2.17.1.chromium15

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-${arch} version:2.17.0.chromium12
+infra/git/windows-${arch} version:2.17.1.chromium15