insertBefore
Insert a node before a given reference node in an element, effectively Node.prototype.insertBefore.
    mutate.insertBefore.call(parent, child, reference)
  
  
  
  Parameters
- parent 
{Node}:The parent into which the child is inserted.
 - child 
{Node}:The child which will be inserted into the parent.
 - reference 
{Node}:The reference which the child will be placed before.
 
Returns
 {Node}: 
The inserted child.