restrict python version for quart

Author: wwwjfy

requirements_dev.txt

@@ -11,7 +11,7 @@ sanic==0.7.0
 aiohttp==3.3.1
 tornado==4.5.3
 async_generator==1.9.0
-quart==0.6.0
+quart==0.6.0;python_version>="3.6"
 
 # tests
 coverage==4.5.1