Fix creating log directory before initializing Logger

`set_configuration` now also assigns Braintree `logger`, but `clear!`
must be called first to create the log directory if it doesn't exist.

lib/fake_braintree.rb

@@ -30,8 +30,8 @@ module FakeBraintree
   def self.activate!(options = {})
     initialize_registry
     self.verify_all_cards = false
-    set_configuration
     clear!
+    set_configuration
     boot_server(port: options.fetch(:gateway_port, nil))
   end