fix(VToolbar): add default width of 100%

this essentially matches systembar and improves pre layout appearance

Author: johnleider

packages/vuetify/src/components/VToolbar/VToolbar.sass

@@ -13,6 +13,7 @@
   position: relative
   transition: $toolbar-transition
   transition-property: height, width, transform, max-width, left, right, top, bottom
+  width: 100%
 
   @include tools.border($toolbar-border...)
   @include tools.elevation($toolbar-elevation)