Bump cffi from 1.15.0 to 1.15.1

Bumps [cffi](http://cffi.readthedocs.org) from 1.15.0 to 1.15.1.

---
updated-dependencies:
- dependency-name: cffi
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements.txt

@@ -14,7 +14,7 @@ async-timeout==3.0.1
     # via aiohttp
 attrs==21.4.0
     # via aiohttp
-cffi==1.15.0
+cffi==1.15.1
     # via pycares
 chardet==4.0.0
     # via aiohttp