[css-transforms-1] Per issue 857, change the initial value of transform-box to view-box.

Author: smfr

css-transforms-1/Overview.bs

@@ -331,7 +331,7 @@ Transform reference box: the 'transform-box' property {#transform-box}
 <pre class='propdef'>
 Name: transform-box
 Value: border-box | fill-box | view-box
-Initial: border-box
+Initial: view-box
 Applies to: [=transformable elements=]
 Inherited: no
 Percentages: N/A