ci: switch to something maintained

See EmbarkStudios/opensource-template#42

.github/workflows/ci.yml

@@ -29,33 +29,21 @@ jobs:
     - uses: actions/checkout@v2
 
     - name: Install ${{ matrix.rust }}
-      uses: actions-rs/toolchain@v1
+      uses: dtolnay/rust-toolchain@master
       with:
           toolchain: ${{ matrix.rust }}
-          override: true
 
     - name: Build
-      uses: actions-rs/cargo@v1
-      with:
-        command: build
+      run: cargo build
 
     - name: Build (with "json" feature)
-      uses: actions-rs/cargo@v1
-      with:
-        command: build
-        args: --features json
+      run: cargo build --features json
 
     - name: Build (with all features)
-      uses: actions-rs/cargo@v1
-      with:
-        command: build
-        args: --all-features
+      run: cargo build --all-features
 
     - name: Build (with no features)
-      uses: actions-rs/cargo@v1
-      with:
-        command: build
-        args: --no-default-features
+      run: cargo build --no-default-features
 
   security-audit:
     runs-on: ubuntu-20.04