add clippy to CI

Author: AaronKutch

.github/workflows/main.yml

@@ -109,6 +109,17 @@ jobs:
     - uses: actions/checkout@v1
       with:
         submodules: true
-    - name: Install Rust
+    - name: Update Stable Rust
       run: rustup update stable && rustup default stable && rustup component add rustfmt
     - run: cargo fmt -- --check
+
+  clippy:
+    name: Clippy
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+      with:
+        submodules: true
+    - name: Update Nightly Rust
+      run: rustup update nightly && rustup default nightly && rustup component add clippy
+    - run: cargo clippy -- -D clippy::all