Add requests to wpt_import vpython spec

Adds the requests module as an entry in
//third_party/blink/tools/wpt_import.py's file-specific vpython spec.
One of the script's dependencies (typ) is taking a dependency on the
requests module, so failing to include it in the vpython spec causes
import failures.

Bug: 1147992
Change-Id: I42258b20373cdb4b3430c8bb01357706ccfb23da
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2544937
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Commit-Queue: Robert Ma <robertma@chromium.org>
Auto-Submit: Brian Sheedy <bsheedy@chromium.org>
Reviewed-by: Robert Ma <robertma@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828396}

third_party/blink/tools/wpt_import.py.vpython

@@ -37,3 +37,10 @@ wheel: <
   name: "infra/python/wheels/six-py2_py3"
   version: "version:1.10.0"
 >
+
+# Not directly used by wpt_import, but required by
+# //third_party/catapult/third_party/typ, which is one of its dependencies.
+wheel: <
+  name: "infra/python/wheels/requests-py2_py3"
+  version: "version:2.13.0"
+>