[bootstrap/win] Release Python 2.7.15

Bug: 879378
Change-Id: Ia8bf1a039b117d87c1caa493cf4b5d93daa69bf9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1666254
Reviewed-by: Marc-Antoine Ruel <maruel@chromium.org>
Commit-Queue: smut <smut@google.com>

bootstrap/win/manifest.txt

@@ -14,7 +14,7 @@
 $VerifiedPlatform windows-386 windows-amd64
 
 @Subdir python
-infra/python/cpython/${platform} version:2.7.13.chromium7
+infra/python/cpython/${platform} version:2.7.15.chromium14
 
 @Subdir git
 infra/git/windows-${arch} version:2.21.0.chromium16