Check if value is an object to properly simple quote value

[ManUtopiK]

Hi!

I fixed a bug that occur only on transformation from AST to markdown when a component has an array attribute.

Input :

::container-component{:items='["Nuxt", "Vue"]'}
::

Before :

::container-component{:items="["Nuxt", "Vue"]"}
::

After this fix :

::container-component{:items='["Nuxt", "Vue"]'}
::

I followed the spec of the JSON string.

I added a bunch of tests around component's attributes...