Bump python2 to 2.7.18

That version was pushed to bleeding_edge in
https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2861642

Bug: 1124119
Change-Id: Id4ab5cb599dc85f3da7784163ddd46b2cd7c7980
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2867872
Auto-Submit: Nico Weber <thakis@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>

bootstrap/manifest.txt

@@ -19,7 +19,7 @@ $VerifiedPlatform windows-amd64 linux-amd64 mac-amd64
 
 # TODO(https://crbug.com/1184768): Remove `=amd64` once mac/arm64 python exists
 @Subdir python
-infra/3pp/tools/cpython/${os}-${arch=amd64} version:2.7.17.chromium.22
+infra/3pp/tools/cpython/${os}-${arch=amd64} version:2@2.7.18.chromium.32
 
 @Subdir python3
 infra/3pp/tools/cpython3/${platform} version:2@3.8.9.chromium.14