[css-flexbox] Fix some link errors.

Author: tabatkins

css-flexbox/Overview.bs

@@ -49,6 +49,9 @@ spec: css-position-3; type: property; text: left
 spec: css-writing-modes-3; type: dfn;
 	text: start
 	text: end
+spec: css-pseudo-4; type: selector;
+	text: ::first-line
+	text: ::first-letter
 </pre>
 
 <style>
@@ -923,7 +926,7 @@ Automatic Minimum Size of Flex Items</h3>
 	However, if the box has an aspect ratio and no <a>specified size</a>,
 	its <a>automatic minimum size</a>
 	is the smaller of its <a>content size</a> and its <a>transferred size</a>.
-	If the box has neither a <a>specified size</a> nor an <a>aspect ratio</a>,
+	If the box has neither a <a>specified size</a> nor an aspect ratio,
 	its <a>automatic minimum size</a> is the <a>content size</a>.
 
 	The <a>content size</a>, <a>specified size</a>, and <a>transferred size</a>