title: Flask template rendering 500 error on zeit
body: <p>Hi I am trying to create my site using Python and Flask, but it returns 500 error.</p>
  
  <pre><code>from flask import Flask
  from flask import render_template
  
  app = Flask(__name__, template_folder='files')
  
  @app.route('/projects')
  def projects():
      return render_template("index.html")
  
  if __name__ == '__main__':
     app.run(debug = True)
  </code></pre>
  
  <p>Folder structure: </p>
  
  <pre><code>appdir
   -myapp.py
   +files
    -index.html
  </code></pre>
  
  <p>Dockerfile:</p>
  
  <pre><code>FROM python:3-alpine
  WORKDIR /usr/src
  COPY requirements.txt .
  RUN pip install -r requirements.txt
  COPY . .
  ENV GUNICORN_CMD_ARGS="--bind=0.0.0.0"
  CMD ["gunicorn", "myapp:app"]
  </code></pre>
  
  <p>Exception:</p>
  
  <pre><code>File "/usr/local/lib/python3.7/site-packages/flask/templating.py", line 86, in _get_source_fast
  10/22 01:38 PM (2m)
      raise TemplateNotFound(template)
  10/22 01:38 PM (2m)
  jinja2.exceptions.TemplateNotFound: index.html
  </code></pre>