Fix people class to persons to entity_name

Author: nontone

lib/pipedrive/base.rb

@@ -60,7 +60,11 @@ def failed_response(res)
     end
 
     def entity_name
-      self.class.name.split('::')[-1].downcase.pluralize
+      class_name = self.class.name.split("::")[-1].downcase.pluralize
+      class_names = {
+        "people" => "persons"
+      }
+      class_names[class_name] || class_name
     end
 
     class << self