Add cargo fmt to build config

.github/workflows/rust.yml

@@ -23,3 +23,18 @@ jobs:
       if: ${{ matrix.rust != '1.34.2' }}
       env:
         FEATURES: ${{ matrix.features }}
+  rustfmt:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - uses: actions-rs/toolchain@v1
+      with:
+        toolchain: stable
+        override: true
+        components: rustfmt
+    - name: Run rustfmt check
+      uses: actions-rs/cargo@v1
+      with:
+        command: fmt
+        args: -- --check
+