Bump version to v0.20.0

Author: jherland

docs/how_to_guides.md

@@ -130,7 +130,7 @@ tool, you can add something like this to your project's
 ```yaml
 repos:
   - repo: https://github.com/tweag/FawltyDeps
-    rev: v0.19.0
+    rev: v0.20.0
     hooks:
       - id: check-undeclared
       - id: check-unused

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "fawltydeps"
-version = "0.19.0"
+version = "0.20.0"
 description = "Find undeclared and unused 3rd-party dependencies in your Python project."
 license = { file = "LICENSE" }
 readme = "README.md"