⬆️ Updates actions/cache action to v2.1.8

Signed-off-by: Renovate Bot <bot@renovateapp.com>

Author: renovate[bot]

.github/workflows/ci.yml

@@ -71,7 +71,7 @@ jobs:
         run: ./gradlew dependencyUpdates -Drevision=release
 
       - name: Cache gradle
-        uses: actions/cache@v2.1.3
+        uses: actions/cache@v2.1.8
         with:
           path: ~/.gradle/caches
           key: ${{ runner.os }}-gradle-${{ hashFiles('checksum.txt') }}
@@ -109,7 +109,7 @@ jobs:
         run: git fetch --unshallow --tags
 
       - name: Cache gradle
-        uses: actions/cache@v2.1.3
+        uses: actions/cache@v2.1.8
         with:
           path: ~/.gradle/caches
           key: ${{ runner.os }}-gradle-${{ hashFiles('checksum.txt') }}
@@ -171,7 +171,7 @@ jobs:
         run: git fetch --unshallow --tags
 
       - name: Cache gradle
-        uses: actions/cache@v2.1.3
+        uses: actions/cache@v2.1.8
         with:
           path: ~/.gradle/caches
           key: ${{ runner.os }}-gradle-${{ hashFiles('checksum.txt') }}