Add ffi-rzmq to runtime dependency in gemspec

Author: kojix2

iruby.gemspec

@@ -21,9 +21,9 @@ Gem::Specification.new do |s|
   s.add_dependency 'multi_json', '~> 1.11'
   s.add_dependency 'mimemagic', '~> 0.3'
   s.add_dependency 'data_uri', '~> 0.1'
+  s.add_dependency 'ffi-rzmq'
 
   s.add_development_dependency 'rake'
   s.add_development_dependency 'minitest'
-  s.add_development_dependency 'ffi-rzmq'
   s.add_development_dependency 'pycall', '>= 1.2.1'
 end