Bump cffi from 1.15.0 to 1.15.1 in /demo/graph_tutorial

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]

demo/graph_tutorial/requirements.txt

@@ -1,6 +1,6 @@
 asgiref==3.5.2
 certifi==2021.10.8
-cffi==1.15.0
+cffi==1.15.1
 chardet==4.0.0
 cryptography==36.0.2
 Django==3.2.13