[api][webui] silence rake/rdoctask is deprecated

silence: "rake/rdoctask is deprecated warning.  Use rdoc/task instead  (in
Roc 2.4.2+)" warning.

This avoids some flooding by the obs-api cronjob:
RAILS_ENV=production rake -s jobs:workerstatus

src/api/Rakefile

@@ -5,7 +5,7 @@ require(File.join(File.dirname(__FILE__), 'config', 'boot'))
 
 require 'rake'
 require 'rake/testtask'
-require 'rake/rdoctask'
+require 'rdoc/task'
 
 require 'tasks/rails'
 begin

src/api/vendor/plugins/acts_as_tree/Rakefile

@@ -1,6 +1,6 @@
 require 'rake'
 require 'rake/testtask'
-require 'rake/rdoctask'
+require 'rdoc/task'
 
 desc 'Default: run unit tests.'
 task :default => :test

src/api/vendor/plugins/classic_pagination/Rakefile

@@ -1,6 +1,6 @@
 require 'rake'
 require 'rake/testtask'
-require 'rake/rdoctask'
+require 'rdoc/task'
 
 desc 'Default: run unit tests.'
 task :default => :test

src/webui/Rakefile

@@ -5,7 +5,7 @@ require(File.join(File.dirname(__FILE__), 'config', 'boot'))
 
 require 'rake'
 require 'rake/testtask'
-require 'rake/rdoctask'
+require 'rdoc/task'
 
 require 'tasks/rails'
 begin

src/webui/vendor/plugins/has_mobile_views/Rakefile

@@ -1,6 +1,6 @@
 require 'rake'
 require 'rake/testtask'
-require 'rake/rdoctask'
+require 'rdoc/task'
 
 desc 'Default: run unit tests.'
 task :default => :test