add beta rust to test jobs

.github/workflows/ci.yml

@@ -12,12 +12,13 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, windows-latest, macOS-latest]
+        rust: [stable, beta]
 
     steps:
       - uses: actions/checkout@v1
       - uses: actions-rs/toolchain@v1
         with:
-          toolchain: stable
+          toolchain: ${{ matrix.rust }}
           override: true
       - name: cargo fetch
         uses: actions-rs/cargo@v1
@@ -77,7 +78,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, windows-latest, macOS-latest]
-        rust: [stable,beta]
+        rust: [stable, beta]
 
     steps:
       - uses: actions/checkout@v1