There is an application that allows you to use specific gestures to issue commands, this may let you enable support for 3 finger gestures. The program is called easystroke. Its in the software center. You can search by the following name: Easystroke Gesture Recognition.
Here is a link to the developers website.
You can also check this already answered question. Which states:
xserver-xorg-input-synaptics is used. It can detect only
2-finger swipes, vertical and horizontal.
There is no code that detects 3-finger swipes. The only way to add
this feature is to code it into the user space driver.
So I guess checking out the application is the better choice.