Calabash IOS ruby installation (rvm) error and solution

echo progress-bar >> ~/.curlrc
execute command to install rvm with latest ruby:
\curl -L https://get.rvm.io | bash -s stable --ruby

Add below line into ~/.bash_profile
#RVM
[[ -s "$HOME/.rvm/scripts/rvm" ]] && source "$HOME/.rvm/scripts/rvm"  # This loads RVM into a shell session.

Check calabash installation
 calabash-ios console
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems.rb:777:in `report_activate_error': Could not find RubyGem json (>= 0) (Gem::LoadError)
from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems.rb:211:in `activate'
from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems.rb:246:in `activate'
from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems.rb:245:in `each'
from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems.rb:245:in `activate'
from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems.rb:1056:in `gem'
from /usr/bin/calabash-ios:18

install this command and you may see below error
sudo gem install json

unable to convert "\xCF" from ASCII-8BIT to UTF-8 for lib/json/ext/generator.bundle,

sudo gem update --system
sudo gem install rdoc