Add cargo clippy to GH Actions

.github/workflows/build.yml

@@ -50,6 +50,19 @@ jobs:
       - name: cargo fmt
         run: cargo fmt -- --check
 
+  clippy:
+    runs-on: ubuntu-18.04
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          override: true
+          components: clippy
+      - name: cargo clippy
+        run: cargo clippy --locked --tests -- -D warnings
+
   test:
     runs-on: ubuntu-18.04
     steps: