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.
recipe_engine:
  https://crrev.com/af7abb5d24a477ca062c054034fe6b5cd44f17c5 [doc] Initial markdown doc generation. (iannucci@chromium.org)


TBR=iannucci@chromium.org

Recipe-Tryjob-Bypass-Reason: Autoroller
Bugdroid-Send-Email: False
Change-Id: Id1169ae5c0d20e1e790aaed824f410f1474b1a12
Reviewed-on: https://chromium-review.googlesource.com/492606
Reviewed-by: <recipe-roller@chromium.org>
Commit-Queue: <recipe-roller@chromium.org>

infra/config/recipes.cfg

@@ -15,7 +15,7 @@
   "deps": {
     "recipe_engine": {
       "branch": "master",
-      "revision": "991fdf7d421a863eff087df095d0fd76b1cf3104",
+      "revision": "af7abb5d24a477ca062c054034fe6b5cd44f17c5",
       "url": "https://chromium.googlesource.com/external/github.com/luci/recipes-py.git"
     }
   },