How to install wpscan on Ubuntu and its derivatives.
I am using Kubuntu, and I found installing wpscan quite a bit of a hustle because *Ubuntu does not have the latest ruby. I have ruby 2.1.5p273 on my system but wpscan requires >=2.1.8.
The best way to upgrade you ruby is to follow the instruction posted here. They have ruby packages upto 2.3, or you can make make install from source.
Then follow the instructions here. That should do the trick.