Log Message:
Update ruby-json and ruby-json-pure to 2.1.0.

## 2017-04-18 (2.1.0)
 * Allow passing of `decimal_class` option to specify a class as which to parse
   JSON float numbers.
## 2017-03-23 (2.0.4)
 * Raise exception for incomplete unicode surrogates/character escape
   sequences. This problem was reported by Daniel Gollahon (dgollahon).
 * Fix arbitrary heap exposure problem. This problem was reported by Ahmad
   Sherif (ahmadsherif).

## 2017-01-12 (2.0.3)
 * Set `required_ruby_version` to 1.9
 * Some small fixes

## 2016-07-26 (2.0.2)
  * Specify `required_ruby_version` for json\_pure.
  * Fix issue #295 failure when parsing frozen strings.

## 2016-07-01 (2.0.1)
  * Fix problem when requiring json\_pure and Parser constant was defined top
    level.
  * Add `RB_GC_GUARD` to avoid possible GC problem via Pete Johns.
  * Store `current_nesting` on stack by Aaron Patterson.

## 2015-09-11 (2.0.0)
  * Now complies to newest JSON RFC 7159.
  * Implements compatibiliy to ruby 2.4 integer unification.
  * Drops support for old rubies whose life has ended, that is rubies < 2.0.
    Also see https://www.ruby-lang.org/en/news/2014/07/01/eol-for-1-8-7-and-1-9-2/
  * There were still some mentions of dual GPL licensing in the source, but JSON
    has just the Ruby license that itself includes an explicit dual-licensing
    clause that allows covered software to be distributed under the terms of
    the Simplified BSD License instead for all ruby versions >= 1.9.3. This is
    however a GPL compatible license according to the Free Software Foundation.
    I changed these mentions to be consistent with the Ruby license setting in
    the gemspec files which were already correct now.