update to 1.2.4

/usr/local/lib/ruby/gems/2.1/gems/cool.io-1.2.1/lib/cool.io/loop.rb:96:
[BUG] Segmentation fault at 0x00000804119b10
ruby 2.1.2p95 (2014-05-08 revision 45877) [amd64-freebsd10]
Merge pull request #260 from reallyenglish/10.0@tomoyukis

update to 1.2.4