add gem 'rake' to integation bundle

Author: kares

src/test/integration/Gemfile

@@ -1,3 +1,7 @@
 source 'https://rubygems.org'
 
-gem 'httpclient', :require => false
+gem 'httpclient', :require => false
+
+group :development do
+  gem 'rake', :require => nil
+end