Add required check step

Fixes #15

Author: zephraph

.github/workflows/build.yml

@@ -4,7 +4,26 @@ on:
   push:
 
 jobs:
+  check:
+    name: Check
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Install Rust
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          override: true
+
+      - name: Cache Rust dependencies
+        uses: Swatinem/rust-cache@v2
+
+      - name: Run cargo check
+        run: cargo check
+
   build:
+    needs: check
     name: Build on ${{ matrix.os }} for ${{ matrix.target }}
     runs-on: ${{ matrix.os }}
     strategy: