[css-syntax-3] Reference identifier-start instead of name-start (w3c#5377)

Author: jonathantneal

css-syntax-3/Overview.bs

@@ -797,7 +797,7 @@ Definitions</h3>
 
 		<dt><dfn export lt="identifier code point | name code point" oldids="name-code-point">identifier code point</dfn>
 		<dd>
-			A <a>name-start code point</a>,
+			An <a>identifier-start code point</a>,
 			a <a>digit</a>,
 			or U+002D HYPHEN-MINUS (-).