解决redis集群安装问题：ruby依赖redis.gem
/usr/local/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:45:in `require': cannot load such file -- redis (LoadError)
from /usr/local/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:45:in `require'
from ./redis-trib.rb:25:in `<main>'
