Tweak coverage of feed exceptions

tests/Feed/TestFeed.php

@@ -5,7 +5,9 @@ use JKingWeb\Arsse\Misc\Date;
 use Phake;
 
 
-/** @covers \JKingWeb\Arsse\Feed */
+/** 
+ * @covers \JKingWeb\Arsse\Feed
+ * @covers \JKingWeb\Arsse\Feed\Exception */
 class TestFeed extends Test\AbstractTest {
     protected static $host = "http://localhost:8000/";
     protected $base = "";