Fix version of actions/cache

.github/workflows/build.yml

@@ -8,7 +8,7 @@ jobs:
   build:
     runs-on: ubuntu-18.04
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v2.3.4
         with:
           repository: openrndr/openrndr
           path: openrndr
@@ -19,7 +19,7 @@ jobs:
       - uses: actions/setup-java@v1
         with:
           java-version: 14
-      - uses: actions/cache@v2.3.4
+      - uses: actions/cache@v2
         with:
           path: |
             ~/.gradle/caches