feat(deps): 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](actions/cache@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/build.yml

@@ -33,7 +33,7 @@ jobs:
           repo-token: ${{ secrets.GITHUB_TOKEN }}
       -
         name: Cache Go modules
-        uses: actions/cache@v1
+        uses: actions/cache@v2.1.6
         with:
           path: |
             ~/go/pkg/mod
@@ -85,7 +85,7 @@ jobs:
           repo-token: ${{ secrets.GITHUB_TOKEN }}
       -
         name: Cache Go modules
-        uses: actions/cache@v1
+        uses: actions/cache@v2.1.6
         with:
           path: |
             ~/go/pkg/mod
@@ -132,7 +132,7 @@ jobs:
           repo-token: ${{ secrets.GITHUB_TOKEN }}
       -
         name: Cache Go modules
-        uses: actions/cache@v1
+        uses: actions/cache@v2.1.6
         with:
           path: |
             ~/go/pkg/mod