Get nightly in build action

.github/workflows/main.yml

@@ -26,6 +26,12 @@ jobs:
       # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
       - uses: actions/checkout@v2
 
+      - name: Install nightly
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: nightly
+          override: true
+
       # Runs a single command using the runners shell
       - name: Build site
         run: |