devel/ruby-msgpack: update to 1.2.4

2018-03-02 version 1.2.3:

* Add Ruby 2.5.0 binary in gem releases for Windows

2018-01-11 version 1.2.2:

* Fix bug to occur SEGV occasionally (depends on GC timing) when exttype is used
* Fix bug to encode an ext type with wrong type id if superclass is also registered as ext type

2017-12-08 version 1.2.1:

* Hotfix release only for JRuby: 1.2.0-java was built in incorrect way

2017-12-07 version 1.2.0:

* Add MessagePack::Factory#dump and MessagePack::Factory#load as convenient methods
  like MessagePack.dump and MessagePack.load
* Fix bug to accept MessagePack::Factory#register_type after #freeze

(taca)