try a CI build with beta rust

.github/workflows/ci.yml

@@ -70,6 +70,33 @@ jobs:
           RUST_BACKTRACE: full
         run: cargo build --verbose --no-default-features
 
+  build-beta:
+    name: Build using rust beta on ${{ matrix.os }}
+    timeout-minutes: 30
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-latest, macOS-latest]
+
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: beta
+          override: true
+      - name: Install LLVM on Windows
+        if: matrix.os == 'windows-latest'
+        run: choco install llvm -y
+      - name: cargo fetch
+        uses: actions-rs/cargo@v1
+        with:
+          command: fetch
+      - name: Build
+        uses: actions-rs/cargo@v1
+        with:
+          command: build
+          args: --verbose --release
+  
   build:
     name: Build on ${{ matrix.os }}
     timeout-minutes: 30