Update GitHub Actions CI (#291)

* update actions/checkout to v3
* update actions/cache to v3
* update actions/upload-artifact to v3
* replace unmaintained actions-rs/toolchain by dtolnay/rust-toolchain

.github/workflows/rust.yml

@@ -27,17 +27,16 @@ jobs:
             release-name: Leafish.app
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
 
       - name: Install Rust
         id: toolchain
-        uses: actions-rs/toolchain@v1
+        uses: dtolnay/rust-toolchain@master
         with:
           toolchain: stable
           components: clippy, rustfmt
-          default: true
 
-      - uses: actions/cache@v2
+      - uses: actions/cache@v3
         with:
           path: |
             ~/.cargo/bin/
@@ -81,7 +80,7 @@ jobs:
           zip -r Leafish.app.zip Leafish.app
 
       - name: Upload binary
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v3
         with:
           name: ${{ matrix.release-name }}
           path: target/release/${{ matrix.target-name }}