Bump actions/cache from v2.1.4 to v2.1.5

Bumps [actions/cache](https://github.com/actions/cache) from v2.1.4 to v2.1.5.
- [Release notes](https://github.com/actions/cache/releases)
- [Commits](actions/cache@v2.1.4...1a9e213)

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/ci.yml

@@ -25,7 +25,7 @@ jobs:
       with:
         ghc-version: ${{ matrix.ghc }}
         cabal-version: 'latest'
-    - uses: actions/cache@v2.1.4
+    - uses: actions/cache@v2.1.5
       name: Cache cabal stuff
       with:
         path: |