weston@Lenovo-Yoga-2-Pro:~$ sudo apt-get purge xserver-xorg-input-synaptics-lts-vivid ; sudo apt-get install --reinstall xserver-xorg-input-synaptics-lts-vivid
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages will be REMOVED:
  xserver-xorg-input-synaptics-lts-vivid*
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
After this operation, 234 kB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 460216 files and directories currently installed.)
Removing xserver-xorg-input-synaptics-lts-vivid (1.8.1-1ubuntu1~trusty1) ...
Processing triggers for man-db (2.6.7.1-1ubuntu1) ...
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Suggested packages:
  gpointing-device-settings touchfreeze
The following NEW packages will be installed:
  xserver-xorg-input-synaptics-lts-vivid
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 0 B/61.3 kB of archives.
After this operation, 234 kB of additional disk space will be used.
Selecting previously unselected package xserver-xorg-input-synaptics-lts-vivid.
(Reading database ... 460198 files and directories currently installed.)
Preparing to unpack .../xserver-xorg-input-synaptics-lts-vivid_1.8.1-1ubuntu1~trusty1_amd64.deb ...
Unpacking xserver-xorg-input-synaptics-lts-vivid (1.8.1-1ubuntu1~trusty1) ...
Processing triggers for man-db (2.6.7.1-1ubuntu1) ...
Setting up xserver-xorg-input-synaptics-lts-vivid (1.8.1-1ubuntu1~trusty1) ...