instal ruby 2.2 on raspberry pi

pi@raspberrypi:~$ curl -L https://get.rvm.io > rvm.sh
pi@raspberrypi:~$ ./rvm.sh  stable --ruby                                                                         
Downloading https://github.com/rvm/rvm/archive/1.26.11.tar.gz                                                     
Downloading https://github.com/rvm/rvm/releases/download/1.26.11/1.26.11.tar.gz.asc
gpg: Signature made Mon 30 Mar 2015 21:52:13 UTC using RSA key ID BF04FF17
gpg: Can't check signature: public key not found     
Warning, RVM 1.26.0 introduces signed releases and automated check of signatures when GPG software found.
Assuming you trust Michal Papis import the mpapis public key (downloading the signatures).
                                                                    
GPG signature verification failed for '/home/pi/.rvm/archives/rvm-1.26.11.tgz' - 'https://github.com/rvm/rvm/relea
ses/download/1.26.11/1.26.11.tar.gz.asc'! 
try downloading the signatures:            
                                     
    gpg --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3  
                                      
or if it fails:                
                                                       
    command curl -sSL https://rvm.io/mpapis.asc | gpg --import -    
                                     
the key can be compared with:          
                                 
    https://rvm.io/mpapis.asc                                     
    https://keybase.io/mpapis  

只好分兩步，先

curl -sSL https://rvm.io/mpapis.asc > mpapis.asc
gpg --import mpapis.asc

重run rvm.sh .. 繼續..