Fix inspector for when default configs are empty

In the beginning of development of a new version, defaults will be
empty.

Author: rafaelfranca

tools/rail_inspector/lib/rail_inspector/configuring/check/framework_defaults.rb

@@ -69,6 +69,7 @@ def app_config_tree
 
           def check_defaults(defaults)
             header, configs = defaults[0], defaults[2, defaults.length - 3]
+            configs ||= []
 
             version = header.match(/\d\.\d/)[0]