ci: fix pre-commit stage

.github/workflows/main.yml

@@ -14,11 +14,16 @@ on:
 jobs:
   pre-commit:
     runs-on: ubuntu-latest
-
     steps:
     - uses: actions/checkout@v2
-    - name: pre-commit
+    - uses: actions/setup-python@v1
-      uses: pre-commit/action@v1.1.0
+    - name: set PY
+      run: echo "::set-env name=PY::$(python -c 'import hashlib, sys;print(hashlib.sha256(sys.version.encode()+sys.executable.encode()).hexdigest())')"
+    - uses: actions/cache@v1
+      with:
+        path: ~/.cache/pre-commit
+        key: pre-commit|${{ env.PY }}|${{ hashFiles('.pre-commit-config.yaml') }}
+    - uses: pre-commit/action@v1.1.0
   lint:
     runs-on: ubuntu-latest