Update default gems list at 8cd6c65af1 [ci skip]

NEWS.md

@@ -155,7 +155,7 @@ The following default gems are updated.
 * securerandom 0.3.0
 * shellwords 0.2.0
 * singleton 0.2.0
-* stringio 3.0.9
+* stringio 3.1.0
 * strscan 3.0.8
 * syntax_suggest 1.1.0
 * tempfile 0.2.0