insert field value in another field value in config yml

[engmagdy87]

in config.yml, I have the following

fields:
      - {
          label: 'Path',
          name: 'path',
          widget: 'hidden',
          default: '/book/{{title}}',
        }
      - { label: 'Title', name: 'title', widget: 'string', required: true }

the generate markdown has
path: '/book/{{title}}'

title wasn't replaced with title text but still on the form of {{title}}

[erquhart]

default should be a plain value, it doesn't expect any expressions. There's an open issue around this: #450