Roll recipe dependencies (trivial).

This is an automated CL created by the recipe roller. This CL rolls recipe
changes from upstream projects (e.g. depot_tools) into downstream projects
(e.g. tools/build).


More info is at https://goo.gl/zkKdpD. Use https://goo.gl/noib3a to file a bug
(or complain)

recipe_engine:
  https://crrev.com/8f704e2ae965ba1aea901c6ee15bf28319fecd83 [doc] Rewrite doc command to produce structured proto directly from python ast. (iannucci@chromium.org)

TBR=iannucci@chromium.org

Change-Id: Idefcac96d647ce0a0cb6465c4be58da0d6b6310c
Recipe-Tryjob-Bypass-Reason: Autoroller
Bugdroid-Send-Email: False
Reviewed-on: https://chromium-review.googlesource.com/455383
Reviewed-by: <recipe-roller@chromium.org>
Commit-Queue: <recipe-roller@chromium.org>

infra/config/recipes.cfg

@@ -4,5 +4,5 @@ deps {
   project_id: "recipe_engine"
   url: "https://chromium.googlesource.com/external/github.com/luci/recipes-py.git"
   branch: "master"
-  revision: "78c57c5d69a38ef3db86d9763d539383f98714e6"
+  revision: "8f704e2ae965ba1aea901c6ee15bf28319fecd83"
 }