Update the number of whole dojos: 1400 -> 1500

> CoderDojo, who recently reached the milestone of having
> 1,500 coding clubs in 75 countries worldwide (2017/10/18)
cf. Celebrating European Code Week with our 5th Annual EU Dojo
https://coderdojo.com/news/2017/10/18/celebrating-european-code-week-with-our-5th-annual-eu-dojo/

Author: yasulab

app/models/dojo.rb

@@ -1,6 +1,6 @@
 class Dojo < ApplicationRecord
   NUM_OF_COUNTRIES    = "75"
-  NUM_OF_WHOLE_DOJOS  = "1,400"
+  NUM_OF_WHOLE_DOJOS  = "1,500"
   NUM_OF_WHOLE_EVENTS = "1,555"
   NUM_OF_JAPAN_DOJOS = Dojo.count.to_s