chore(examples): pin suckerpunch path in example config.ru

example/Gemfile

@@ -4,3 +4,4 @@ gem "pact_broker" # Would pin this to a known minor version when using properly
 gem "puma", "~> 5.3" # Can be replaced with your choice of application server
 gem "sqlite3", "~>1.3" # Sqlite is just for testing. Replace this with "pg" for production.
 # gem "pg" # Production database gem
+gem "sucker_punch", git: "https://github.com/pact-foundation/sucker_punch.git", ref: "fix/rename-is-singleton-class-method-2"