Move custom error to module it is used in

lib/sentry/client.rb

@@ -10,7 +10,6 @@ module Sentry
 
     Error = Class.new(StandardError)
     MissingKeysError = Class.new(StandardError)
-    ResponseInvalidSizeError = Class.new(StandardError)
 
     attr_accessor :url, :token
 

lib/sentry/client/issue.rb

@@ -4,6 +4,7 @@ module Sentry
   class Client
     module Issue
       BadRequestError = Class.new(StandardError)
+      ResponseInvalidSizeError = Class.new(StandardError)
 
       SENTRY_API_SORT_VALUE_MAP = {
         # <accepted_by_client> => <accepted_by_sentry_api>