Build docs on nightly

Author: davidcole1340

.github/workflows/docs.yml

@@ -38,13 +38,10 @@ jobs:
         with:
           mdbook-version: latest
       - name: Build docs
-        uses: actions-rs/cargo@v1
         env:
           LIBCLANG_PATH: ${{ runner.temp }}/llvm-${{ matrix.llvm }}/lib
           RUSTDOCFLAGS: --cfg docs
-        with:
-          command: doc
-          args: --release
+        run: cargo +nightly doc --release
       - name: Build guide
         run: |
           mdbook build guide