Not running on CentOS

[giriji]

Following error shows up ... On CentOS 6.9 & ruby 1.8.7
[root@server HatCloud]# ruby hatcloud.rb -h
hatcloud.rb:64: warning: don't put space before argument parentheses
hatcloud.rb:81: warning: don't put space before argument parentheses
hatcloud.rb:5:in `require': no such file to load -- json (LoadError)
from hatcloud.rb:5