Update default gems list at 87d32376d9 [ci skip]

NEWS.md

@@ -436,6 +436,7 @@ Note: We're only listing outstanding class updates.
     * psych 5.0.1
     * racc 1.6.1
     * rdoc 6.5.0
+    * readline-ext 0.1.5
     * reline 0.3.1
     * resolv 0.2.2
     * securerandom 0.2.1