title: GitHub Actions Upload Artifact not finding provided path from npm run build
body: <p>I'm trying to set up a react website using CICD principles. I can run it locally, use 'npm run build' to get a build folder, and the website works fine when I manually push the files to S3. However, when I try to run the build and deployment through github actions, the upload-artifacts step gives the following warning: 'Warning: No files were found with the provided path: build. No artifacts will be uploaded.' Obviously the deploy job then fails since it can't find any artifacts to download. Why exactly is this happening? The build folder is definitely being created since running ls after the build lists it as one of the folders in the current working directory.</p>
  <pre><code>name: frontend_actions
  on:
    workflow_dispatch:
    push:
      paths:
        - 'frontend/'
        - '.github/workflows/frontend_actions.yml'
      branches:
        - master
  defaults:
    run:
      working-directory: frontend
  jobs:
    build:
      runs-on: ubuntu-latest
      steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-node@v2
      - name: npm install
        run: npm install
      - name: npm build
        run: npm run build
        env:
          CI: false
      - name: Upload Artifact
        uses: actions/upload-artifact@master
        with:
          name: build
          path: build
    deploy:
      needs: build
      runs-on: ubuntu-latest
      steps:
        - uses: actions/checkout@v2
        - name: Download Artifact
          uses: actions/download-artifact@master
          with:
            name: build
            path: build
        - name: Deploy to S3
          uses: jakejarvis/s3-sync-action@master
          with:
            args: --acl public-read --follow-symlinks --delete
          env:
            AWS_S3_BUCKET: ${{ secrets.AWS_S3_BUCKET }}
            AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_ID }}
            AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
            AWS_REGION: 'us-west-2'   # optional: defaults to us-east-1
            SOURCE_DIR: 'build'   # optional: defaults to entire repository
  </code></pre>