Create task to update js files automatically

Rakefile

@@ -1,2 +1,13 @@
 require 'bundler'
 Bundler::GemHelper.install_tasks
+
+namespace :d3 do
+  desc 'Update d3 version'
+  task :update_version do
+    `curl -o app/assets/javascripts/d3.js https://raw.githubusercontent.com/mbostock/d3/master/d3.js`
+    `curl -o app/assets/javascripts/d3.min.js https://raw.githubusercontent.com/mbostock/d3/master/d3.min.js`
+    `cp app/assets/javascripts/d3.js app/assets/javascripts/d3.v3.js`
+    `cp app/assets/javascripts/d3.min.js app/assets/javascripts/d3.v3.min.js`
+    puts "Update manually version to #{`grep 'version: ".*"' app/assets/javascripts/d3.js | cut -d '"' -f 2`}CHANGELOG.md\nREADME.md\nlib/d3/rails/version.rb\n"
+  end
+end