add doc check in CI

.github/workflows/ci.yml

@@ -73,6 +73,21 @@ jobs:
           command: fmt
           args: --all -- --check
 
+  check-doc:
+    name: Check Documentation Build
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: nightly
+          override: true
+          profile: minimal
+      - uses: actions-rs/cargo@v1
+        with:
+          command: doc
+          args: --all-features
+
   clippy:
     name: Clippy
     runs-on: ubuntu-latest