[css-break] Fix bracketed range grammar to match prose w3c#8247

Author: fantasai

css-break-3/Overview.bs

@@ -449,7 +449,7 @@ Breaks Between Lines: 'orphans', 'widows'</h3>
 
   <pre class="propdef">
   Name: orphans, widows
-  Value: <<integer [0,∞]>>
+  Value: <<integer [1,∞]>>
   Initial: 2
   Applies to: <a>block containers</a> that establish an <a>inline formatting context</a>
   Inherited: yes

css-break-4/Overview.bs

@@ -445,7 +445,7 @@ Breaks Between Lines: 'orphans', 'widows'</h3>
 
 	<pre class="propdef">
 	Name: orphans, widows
-	Value: <<integer [0,∞]>>
+	Value: <<integer [1,∞]>>
 	Initial: 2
 	Applies to: <a>block containers</a> that establish an <a>inline formatting context</a>
 	Inherited: yes