Update sanic from 0.8.3 to 18.12.0 (#416)

Author: pyup-bot

requirements_dev.txt

@@ -5,7 +5,7 @@ bumpversion==0.5.3  # pyup: update minor
 wheel==0.32.2  # pyup: update minor
 cryptography==2.4.1  # pyup: update minor
 psycopg2-binary==2.7.6.1  # pyup: update minor
-sanic==0.8.3  # pyup: update minor
+sanic==18.12.0  # pyup: update minor
 aiohttp==3.5.0  # pyup: update minor
 tornado==5.1.1  # pyup: update minor
 async_generator==1.10  # pyup: update minor