从1.8.7 升级到 2.1.1

step 1 download tar.gz package

step2  unpack tar -zxvf xxx.tar.gz

step3 cd ruby2.1.1.dir

step4 .configure

step5 make

step6 sudo make install

step7 remove 1.8.7 : sudo apt-get remove ruby1.8.7

done