fix(list): removes outline from focus state (#511)

Author: robertmesserle

src/components/list/list.scss

@@ -202,6 +202,7 @@ md-nav-list {
     cursor: pointer;
 
     &:hover, &.md-list-item-focus {
+      outline: none;
       background: md-color($md-background, 'hover');
     }
   }