Bump actions/cache from 1 to 2.1.6

Bumps [actions/cache](https://github.com/actions/cache) from 1 to 2.1.6.
- [Release notes](https://github.com/actions/cache/releases)
- [Commits](https://github.com/actions/cache/compare/v1...v2.1.6)

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

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

.github/workflows/static.yml

@@ -16,7 +16,7 @@ jobs:
     - uses: actions/setup-node@v2.4.1
 
     - name: Cache node modules
-      uses: actions/cache@v1
+      uses: actions/cache@v2.1.6
       env:
         cache-name: cache-node-modules
       with:
@@ -25,7 +25,7 @@ jobs:
 
     - name: Cache validator
       id: validator-cache
-      uses: actions/cache@v1
+      uses: actions/cache@v2.1.6
       with:
         path: vnu-runtime-image
         key: ${{ runner.os }}-validator-${{ env.VALIDATOR_VERSION }}