Print author details for a node
This is what worked for me in the node template for any custom field:

{{ node.uid.entity.field_name.value }}


I'm using Drupal 8.3.7

EDIT:
This is what I'm doing for the profile picture. 
I'm creating a rendering object so I can specify a theme and an image style:

            {% set imagestyle = {
              '#theme':      'image_style',
              '#style_name': 'user_avatar_80x80',
              '#uri':        node.uid.entity.user_picture.entity.uri.value,
              '#attributes': { class: 'authorImg' },
            } %}
            &lt;div class="authorCol1"&gt;{{ imagestyle }}&lt;/div&gt;