Change create_calsses to a class_name

lib/weather/model.rb

@@ -4,7 +4,7 @@ module Weather
   module Model
 
     require 'source_schema'
-    def create_classes
+    def self.create_classes
       Weather::Model::SourceSchema.each do |source|
         Object.const_set("#{source}::Mysql", Class.new(Source::Mysql))
         Object.const_set("#{source}::Ohm", Class.new(Source::Ohm))