[CircleCI] build-1604: restore pytorch cache instead of obsolete ATen

8a80728 (Sun Apr 22 08:54:09 2018
-0700) replaced ATen submodule with PyTorch submodule and updated the
CircleCI configuration except for restoring ATen compilation cache in
1604 configuration: it attempts to take the hash of a no longer existing
submodule ATen.  As a result, this configuration attempts to load from
non-existent cache, fails and has to recompile ATen every time.  Take
the hash of the pytorch submodule instead since ATen now comes from
there.  Storing to compilation cache already uses the pytorch hash.

Author: ftynse

.circleci/config.yml

@@ -137,7 +137,7 @@ jobs:
 
       - restore_cache:
           keys:
-            - v1-aten-{{ checksum ".git/modules/third-party/ATen/HEAD" }}-{{ checksum "build.sh" }}-{{ checksum ".circleci/config.yml" }}-{{ arch }}-1604
+            - v1-aten-{{ checksum ".git/modules/third-party/pytorch/HEAD" }}-{{ checksum "build.sh" }}-{{ checksum ".circleci/config.yml" }}-{{ arch }}-1604
 
       - restore_cache:
           keys: