Dup as_json options if frozen (#625)

Co-authored-by: Christopher Nelson <chris@chrisnelson.au>

Author: chrisrbnelson

lib/quickbooks/model/base_model.rb

@@ -30,6 +30,7 @@ def to_xml_inject_ns(model_name, options = {})
 
       def as_json(options = nil)
         options = {} if options.nil?
+        options = options.dup if options.frozen?
         except_conditions = ["roxml_references"]
         except_conditions << options[:except]
         options[:except] = except_conditions.flatten.uniq.compact