Bump actions/cache from 2.1.5 to 2.1.6

Bumps [actions/cache](https://github.com/actions/cache) from 2.1.5 to 2.1.6.
- [Release notes](https://github.com/actions/cache/releases)
- [Commits](actions/cache@v2.1.5...v2.1.6)

---
updated-dependencies:
- dependency-name: actions/cache
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/lint.yml

@@ -18,7 +18,7 @@ jobs:
         uses: actions/[email protected]
         with:
           python-version: ${{ matrix.python-version }}
-      - uses: actions/[email protected].5
+      - uses: actions/[email protected].6
         id: pip-cache
         with:
           path: ~/.cache/pip