Fix cache names in CircleCI jobs
# What does this PR do?

Fix cache names in CircleCI jobs.

According to [this doc](https://circleci.com/docs/caching#restoring-cache), the cache names in `CircleCI` jobs should follow the patterns:
```yaml
- restore_cache:
      keys:
          - v0.5-torch-{{ checksum "setup.py" }}
          - v0.5-torch-
- save_cache:
      key: v0.5-torch-{{ checksum "setup.py" }}
      paths:
          - '~/.cache/pip'  
```

- The 2nd key in `restore_cache` should be the 1st key without `{{ checksum "setup.py" }}`
- The key in `save_cache` should be the 1st key in `restore_cache`

We need the trailing `-` in the 2nd key in `restore_cache` to avoid the collapse between `v0.5-torch-` and `v0.5-torch_and_tf-` ect.

(Thanks @stas00 for finding this issue, and @gante for the comment on Slack)
_The documentation is not available anymore as the PR was closed or merged._