[recipes.cfg] Update recipes.cfg to new canonical recipe URL.

R=agable@chromium.org, dnj@chromium.org, vadimsh@chromium.org

Bug: 726507
Change-Id: I613e993b5ac3ea80c2c4679b7efcd3e0b291f91b
Reviewed-on: https://chromium-review.googlesource.com/607161
Reviewed-by: Erik Staab <estaab@chromium.org>

infra/config/recipes.cfg

@@ -16,7 +16,7 @@
     "recipe_engine": {
       "branch": "master",
       "revision": "e92def4f3c06e6dc65c8d69f6bbb378ccba92546",
-      "url": "https://chromium.googlesource.com/external/github.com/luci/recipes-py.git"
+      "url": "https://chromium.googlesource.com/infra/luci/recipes-py.git"
     }
   },
   "project_id": "depot_tools",