Bump beautifulsoup4 from 4.8.2 to 4.9.1

Bumps [beautifulsoup4](http://www.crummy.com/software/BeautifulSoup/bs4/) from 4.8.2 to 4.9.1.

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Author: dependabot-preview[bot]

requirements.txt

@@ -1,7 +1,7 @@
 aiohttp==3.6.2
 async-timeout==3.0.1
 attrs==19.3.0
-beautifulsoup4==4.8.2
+beautifulsoup4==4.9.1
 bs4==0.0.1
 certifi==2019.11.28
 chardet==3.0.4