make sure cargo is installed

Author: olback

.github/workflows/macos.yml

@@ -9,6 +9,11 @@ jobs:
 
     steps:
     - uses: actions/checkout@v1
+    - name: Install latest stable
+      uses: actions-rs/toolchain@v1
+      with:
+          toolchain: stable
+          override: true
     - uses: actions-rs/cargo@v1
       with:
         command: build