Verify MSRV in CI

.github/workflows/rust.yml

@@ -39,6 +39,20 @@ jobs:
           command: test
           args: --no-default-features
 
+  msrv:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: "1.63.0"
+          override: true
+      - uses: actions-rs/cargo@v1
+        with:
+          command: check
+          args: --lib --all-features
+
   lint:
     runs-on: ubuntu-latest
     steps: