Update R-CMD-check.yaml

clear package cache as suggested by @hsbadr in #514 (comment)

Author: jgabry

.github/workflows/R-CMD-check.yaml

@@ -57,8 +57,8 @@ jobs:
         uses: actions/cache@v2
         with:
           path: ${{ env.R_LIBS_USER }}
-          key: ${{ runner.os }}-${{ hashFiles('.github/R-version') }}-1-${{ hashFiles('.github/depends.Rds') }}
-          restore-keys: ${{ runner.os }}-${{ hashFiles('.github/R-version') }}-1-
+          key: ${{ runner.os }}-${{ hashFiles('.github/R-version') }}-2-${{ hashFiles('.github/depends.Rds') }}
+          restore-keys: ${{ runner.os }}-${{ hashFiles('.github/R-version') }}-2-
 
       - name: Install system dependencies
         if: runner.os == 'Linux'