Update quart from 0.8.0 to 0.9.1 (#482)

Author: pyup-bot

requirements_dev.txt

@@ -9,7 +9,7 @@ sanic==19.3.1  # pyup: update minor
 aiohttp==3.5.0  # pyup: update minor
 tornado==6.0  # pyup: update minor
 async_generator==1.10  # pyup: update minor
-quart==0.8.0;python_version>="3.7"  # pyup: update minor
+quart==0.9.1;python_version>="3.7"  # pyup: update minor
 
 # tests
 coverage==4.5.1  # pyup: update minor