Test on multiple rust versions

.github/workflows/ci.yml

@@ -3,8 +3,17 @@ on: [ push, pull_request ]
 jobs:
   build:
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        include:
+          - { rust: nightly }
+          - { rust: stable }
     steps:
       - uses: actions/checkout@v3
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: ${{ matrix.rust }}
+          override: true
       - name: Build
         run: cargo build
       - name: Test