use eventmachine at github master

because eventmachine 1.0.3 cannot compile on ruby 2.2.0

ttps://github.com/eventmachine/eventmachine/commit/c95f1e11c2c0f0e23cd9d4ac2a9c7a75afe54710
Merge pull request #195 from onk/feature/support_ruby_2_2_0

use eventmachine at github master