This gem behavior is not same as method_source when invoke proc.source

Following just a example:

When use `fast_method_source`, i only can get block first line.

```rb
add_job_into_delayed_worker job_name: 'simple delayed worker' do
```

But, when use `method_source`, i can get full blocked content.

```rb
    add_job_into_delayed_worker job_name: 'simple delayed worker' do
      $stdout.print 'delayed worker is run!'    
    end
```