Update default gems list at 811bc15 [ci skip]

Author: matzbot

NEWS.md

@@ -172,7 +172,7 @@ The following default gems are updated.
 * io-nonblock 0.3.1
 * ipaddr 1.2.7
 * irb 1.14.1
-* json 2.8.2
+* json 2.9.0
 * logger 1.6.2
 * net-http 0.6.0
 * open-uri 0.5.0