stack-in-card: 'keep: margin: false' is not respected for inserted stack

Checklist:

• [x ] I updated to the latest version available
• [x ] I cleared the cache of my browser

Release with the issue: 0.2.0

Last working release (if known):

Browser and Operating System: Chrome, Win10x64

Description of problem:

If the ‘keep: margin: false’ is set then the margin between card is supposed to be 0. It works for two Entities cards:

  - type: custom:stack-in-card
    mode: vertical
    keep:
      background: true
      box_shadow: false
      margin: false
      outer_padding: false
      border_radius: false
    cards:
     - type: entities
       entities:
         - sun.sun
       card_mod:
         style: |
           ha-card {
             background-color: red;
           }
     - type: entities
       entities:
         - sun.sun
       card_mod:
         style: |
           ha-card {
             background-color: green;
           }

But if the 2nd card is stack-in-card, then the margin is present anyway - look at the margin-top:

  - type: custom:stack-in-card
    mode: vertical
    keep:
      background: true
      box_shadow: false
      margin: false
      outer_padding: false
      border_radius: false
    cards:
     - type: entities
       entities:
         - sun.sun
       card_mod:
         style: |
           ha-card {
             background-color: red;
           }
     - type: custom:stack-in-card
       mode: horizontal
       keep:
         background: true
         box_shadow: false
         margin: false
         outer_padding: false
         border_radius: false
       cards:
         - type: entities
           entities:
             - sun.sun
           card_mod:
             style: |
               ha-card {
                 background-color: red;
               }
         - type: entities
           entities:
             - sun.sun
           card_mod:
             style: |
               ha-card {
                 background-color: green;
               }

Javascript errors shown in the web inspector (if applicable): no

Additional information: