cannot make rails app in my directory

i have problem when try create new apps in rails,
i type rails new coba, then the respon is

Fetching source index for https://rubygems.org/
Using rake (0.9.2.2)
Using i18n (0.6.0)
Using multi_json (1.3.1)
Using activesupport (3.2.1)
Using builder (3.0.0)

Gem::RemoteFetcher::FetchError: Errno::ETIMEDOUT: A connection attempt
failed because the connected party did not properly respond after
a period of time, or established connection failed because connected
host has failed to respond. - connect(2) (https://rubygems.org/quick
/Marshal.4.8/activemodel-3.2.1.gemspec.rz)
An error occured while installing activemodel (3.2.1), and Bundler
cannot continue.
Make sure that `gem install activemodel -v '3.2.1'` succeeds before
bundling.

HELP ME please