[flori/json] Bump JSON::VERSION to 2.6.0.

https://github.com/flori/json/commit/da94d9f059

ext/json/lib/json/version.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: false
 module JSON
   # JSON version
-  VERSION         = '2.5.1'
+  VERSION         = '2.6.0'
   VERSION_ARRAY   = VERSION.split(/\./).map { |x| x.to_i } # :nodoc:
   VERSION_MAJOR   = VERSION_ARRAY[0] # :nodoc:
   VERSION_MINOR   = VERSION_ARRAY[1] # :nodoc: