Fix path matching in match-url-to-source-expression (#773)

Author: antosart

index.bs

@@ -4077,8 +4077,7 @@ Content-Type: application/reports+json
       6.  If |expression| contains a non-empty <a grammar>`path-part`</a>, and
           |redirect count| is 0, then:
 
-          1.  Let |path| be the resulting of joining |url|'s <a for="url">path</a>
-              on the U+002F SOLIDUS character (`/`).
+          1.  Let |path| be the result of running the <a>URL path serializer</a> on |url|.
 
           2.  If |expression|'s <a grammar>`path-part`</a> does not <a>`path-part` match</a> |path|,
               return "`Does Not Match`".