add cache to the ci

.github/workflows/rust.yml

@@ -22,6 +22,13 @@ jobs:
         os: [ubuntu-18.04, macos-latest, windows-latest]
     steps:
     - uses: actions/checkout@v2
+    - name: Cache dependencies
+      uses: actions/cache@v2
+      with:
+        path: |
+          ~/.cargo
+          ./target
+        key: ${{ matrix.os }}-${{ hashFiles('Cargo.lock') }}
     - name: Run cargo check without any default features
       uses: actions-rs/cargo@v1
       with:
@@ -38,6 +45,13 @@ jobs:
     runs-on: ubuntu-18.04
     steps:
       - uses: actions/checkout@v2
+      - name: Cache dependencies
+        uses: actions/cache@v2
+        with:
+          path: |
+            ~/.cargo
+            ./target
+          key: ${{ matrix.os }}-${{ hashFiles('Cargo.lock') }}
       - uses: actions-rs/toolchain@v1
         with:
           profile: minimal
@@ -55,6 +69,13 @@ jobs:
     runs-on: ubuntu-18.04
     steps:
       - uses: actions/checkout@v2
+      - name: Cache dependencies
+        uses: actions/cache@v2
+        with:
+          path: |
+            ~/.cargo
+            ./target
+          key: ${{ matrix.os }}-${{ hashFiles('Cargo.lock') }}
       - uses: actions-rs/toolchain@v1
         with:
           profile: minimal