Bump actions/cache from 2.1.5 to 2.1.6 (#16)

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)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/github-pages.yml

@@ -26,7 +26,7 @@ jobs:
         run: echo "::set-output name=dir::$(pip cache dir)"
 
       - name: Cache dependencies
-        uses: actions/[email protected].5
+        uses: actions/[email protected].6
         with:
           path: ${{ steps.pip-cache.outputs.dir }}
           key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements.txt') }}