fix cudnn version in main & min gpu version

Author: sunjiahao1999

.circleci/test.yml

@@ -174,6 +174,7 @@ workflows:
           # Use double quotation mark to explicitly specify its type
           # as string instead of number
           cuda: "10.2"
+          cudnn: 7
           requires:
             - hold
       - build_cuda:
@@ -191,6 +192,7 @@ workflows:
           name: minimum_version_gpu
           torch: 1.8.1
           cuda: "10.2"
+          cudnn: 7
           filters:
             branches:
               only: