Fix module name error

lib/rucaptcha.rb

@@ -40,7 +40,7 @@ module RuCaptcha
       length = config.length
 
       unless length.in?(3..7)
-        raise Rucaptcha::Errors::Configuration, 'length config error, value must in 3..7'
+        raise RuCaptcha::Errors::Configuration, 'length config error, value must in 3..7'
       end
 
       strikethrough = config.strikethrough ? 1 : 0

lib/rucaptcha/errors/configuration.rb

@@ -1,4 +1,4 @@
-module Rucaptcha
+module RuCaptcha
   module Errors
     class Configuration < StandardError; end
   end