ci: Use dtonlnay runner for WASM

Use the newer github action cargo runner from dtolnay.

Note, with this applied we only run the WASM tests using the stable
toolchain.

.github/workflows/rust.yml

@@ -58,21 +58,13 @@ jobs:
   WASM:
     name: WASM
     runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        rust: [stable, beta, nightly] # wasm-pack doesn't support rust 1.41.1
     steps:
       - name: Checkout Crate
         uses: actions/checkout@v2
       - name: Install clang
         run: sudo apt-get install -y clang
       - name: Checkout Toolchain
-        uses: actions-rs/toolchain@v1
-        with:
-          profile: minimal
-          toolchain: ${{ matrix.rust }}
-          override: true
-          components: rust-src
+        uses: dtolnay/rust-toolchain@stable
       - name: Running WASM tests
         env:
           DO_WASM: true