[MdListExpand] expand content cursor style

[VdustR]

Steps to reproduce

Expand the expandable list item, move the cursor into .md-list-expand.

Which browser?

All browsers.

Vue Material v1.0.0-beta-8

What is expected?

pointer cursor should only show in .md-list-item-content.

default cursor should show in .md-list-expand

What is actually happening?

pointer cursor show in whole .md-list-item-container

Structure:

.md-list-item-container
  .md-list-item-content
  .md-list-expand

hover background color is bound on .md-list-item-container too.

Reproduction Link

Offcial documentation: https://vuematerial.io/components/list