use dtolnay/rust-toolchain rather than unmaintained actions-rs/toolchain

Author: micolous

.github/workflows/rust.yml

@@ -25,10 +25,9 @@ jobs:
     steps:
     - uses: actions/checkout@v2
     - name: Install toolchain
-      uses: actions-rs/toolchain@v1
-      with:
-        toolchain: ${{ matrix.toolchain }}
-        override: true
+      uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ matrix.toolchain }}
     - name: Build
       run: cargo build --verbose
     - name: Run tests