[css-rhythm-1] Update references to block-step-insert: margin

Author: nt1m

css-rhythm-1/Overview.bs

@@ -267,7 +267,7 @@ Specifying Alignment: the 'block-step-align' property {#block-step-align}
 	<dl dfn-for="block-step-align" dfn-type="value">
 		<dt><dfn>auto</dfn>
 		<dd>
-			If 'block-step-insert' is ''margin'':
+			If 'block-step-insert' is ''margin-box'':
 			if 'align-self' is ''start'', ''end'', or ''center'', treat as that value,
 			otherwise treat as ''center''.
 
@@ -289,7 +289,7 @@ Specifying Alignment: the 'block-step-align' property {#block-step-align}
 	additional spacing cannot be added to margins
 	that are truncated or omitted due to unforced fragmentation breaks
 	(see [[CSS3-PAGE]] and [[CSS-BREAK-3]]);
-	therefore if 'block-step-insert' is ''margin'',
+	therefore if 'block-step-insert' is ''margin-box'',
 	all extra space derived from applying 'block-step-size'
 	must be inserted on the opposite side of the fragment
 	(regardless of 'block-step-align').