ci: update actions/cache to v2

.github/workflows/ci.yml

@@ -30,19 +30,19 @@ jobs:
         override: true
 
     - name: Cache cargo registry
-      uses: actions/cache@v1
+      uses: actions/cache@v2
       with:
         path: ~/.cargo/registry
         key: ${{ matrix.os }}-${{ matrix.rust }}-cargo-registry-${{ hashFiles('**/Cargo.toml') }}
 
     - name: Cache cargo index
-      uses: actions/cache@v1
+      uses: actions/cache@v2
       with:
         path: ~/.cargo/git
         key: ${{ matrix.os }}-${{ matrix.rust }}-cargo-index-${{ hashFiles('**/Cargo.toml') }}
 
     - name: Cache cargo build
-      uses: actions/cache@v1
+      uses: actions/cache@v2
       with:
         path: target
         key: ${{ matrix.os }}-${{ matrix.rust }}-cargo-build-target-${{ hashFiles('**/Cargo.toml') }}