improve: add rake/common/dsl module

For rake > v0.8.7 we can see error 'uninitialized constant Rake::DSL'.
To avoid this error we must include something like that onto top of Rakefile

    if RAKEVERSION !~ /^0\.8/
        require 'rake/dsl_definition'
        include Rake::DSL
        Rake::TaskManager.record_task_metadata = true if Rake::TaskManager.respond_to?('record_task_metadata')
    end

To avoid duplicity of code we can just add
    require 'rake/common/dsl'