Add Ruby 2.2 to continuous integration
Add Ruby 2.2 to continuous integration

Since 2.1 was just added, might as well add 2.2 also
liangsun/discount,liangsun/rdiscount,liangsun/discount,liangsun/rdiscount,liangsun/discount,liangsun/discount,liangsun/discount,liangsun/rdiscount,liangsun/rdiscount