fix: Correct cloudevents dependency to allow 1.11.0 (GoogleCloudPlatform#405)

Python 3.7 is no longer supported so don't allow versions prior to
1.11.0 but allow 1.11.0 as Python 3.8 is still supported by the
framework.

Author: maemayve

pyproject.toml

@@ -27,7 +27,7 @@ dependencies = [
   "click>=7.0,<9.0",
   "watchdog>=1.0.0",
   "gunicorn>=22.0.0; platform_system!='Windows'",
-  "cloudevents>=1.12.0,<=1.12.0",                   # Must support python 3.7
+  "cloudevents>=1.11.0,<=1.12.0",                   # Must support python 3.8
   "Werkzeug>=0.14,<4.0.0",
   "starlette>=0.37.0,<1.0.0; python_version>='3.8'",
   "uvicorn>=0.18.0,<1.0.0; python_version>='3.8'",