[BUGFIX] Use xDebug for PHP 5.6

The PHP version has been upgraded to version 5.6 but xDebug was
still version 5.5 compatible.

recipes/default.rb

@@ -34,7 +34,7 @@ if node['platform_version'] == '16.04'
 		notifies :restart, 'service[apache2]', :delayed
 	end
 else
-	package 'php5-xdebug'
+	package 'php5.6-xdebug'
 
 	template '/etc/php5/apache2/conf.d/xdebug.ini' do
 		mode '0644'