Add cd into example

Author: GroovinChip

.github/workflows/gh_pages.yml

@@ -16,7 +16,9 @@ jobs:
         with:
           channel: stable
       - run: flutter pub get
-      - run: flutter build web
+      - run: |
+          cd example
+          flutter build web
       - name: Archive Production Artifact
         uses: actions/upload-artifact@master
         with: