I was not able to install capybara-webkit gem on Ubuntu 16.04. I tried to follow the instructions mentioned in the gem wiki to solve this problem.

sudo apt-get update
sudo apt-get install g++ qt5-default libqt5webkit5-dev gstreamer1.0-plugins-base gstreamer1.0-tools gstreamer1.0-x

Then it gave an error saying that the package is not installable.

The following packages have unmet dependencies:
 qtbase5-dev : Depends: libgles2-mesa-dev or
                        libgles2-dev but it is not installable                        
                      

Looks like Ubuntu 16.04 is not supporting that package anymore.

I was able to fix this error by running following command:

sudo apt-get install qt-sdk

After this, the bundle install completed successfully and installed the capybara-webkit gem.

Note that this uses Qt 4 and not Qt 5.

I have updated the capybara-webkit wiki with this solution.