Update default gems list at 30632ef [ci skip]

Author: matzbot

NEWS.md

@@ -158,7 +158,7 @@ Note: We're only listing outstanding class updates.
     * ostruct 0.5.5
     * reline 0.3.1
     * securerandom 0.2.0
-    * stringio 3.0.2
+    * stringio 3.0.3
 *   The following bundled gems are updated.
     * net-imap 0.2.3
     * rbs 2.4.0