Fix broken links

Closes #1168

Author: frivoal

css-ui-4/Overview.bs

@@ -921,8 +921,8 @@ Omitted values are set to their initial values.
 
 	For the purpose of this specification,
 	an <dfn>editable element</dfn> is either
-	an <a href="https://dvcs.w3.org/hg/editing/raw-file/tip/editing.html#editing-host">editing host</a>
-	or a <a href="https://www.w3.org/TR/html/forms.html#mutability">mutable</a> form control with textual content,
+	an <a href="https://w3c.github.io/editing/contentEditable.html#dfn-editing-host">editing host</a>
+	or a <a href="https://www.w3.org/TR/html/sec-forms.html#mutable">mutable</a> form control with textual content,
 	such as <{textarea}>.
 
 	Issue: Should there be constraints