ci: add rust cache

Author: Enter-tainer

.github/workflows/build.yml

@@ -24,6 +24,7 @@ jobs:
         with:
           command: build
           args: --release
+      - uses: Swatinem/rust-cache@v1
       - uses: actions/upload-artifact@v2
         with:
           name: ${{ matrix.asset_name }}