Ensure downward compatability

Switching to old import workflow on werkzeug when new workflow fails.

Author: Nicolas Neuburger

demo_app/app.py

@@ -4,7 +4,10 @@
 
 from flask import Flask, render_template
 from werkzeug.serving import run_simple
-from werkzeug.middleware.dispatcher import DispatcherMiddleware
+try:
+    from werkzeug.middleware.dispatcher import DispatcherMiddleware
+except ImportError:
+    from werkzeug.wsgi import DispatcherMiddleware
 
 from flasgger import __version__
 from flasgger.utils import get_examples