Bump actions/cache from 2 to 2.1.5

Bumps [actions/cache](https://github.com/actions/cache) from 2 to 2.1.5.
- [Release notes](https://github.com/actions/cache/releases)
- [Commits](actions/cache@v2...v2.1.5)

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/cache@v2
+      - uses: actions/cache@v2.1.5
         id: pip-cache
         with:
           path: ~/.cache/pip