fix lcov support
fix lcov support

Ubuntu 18.10 comes with lcov 1.13, which is now added.

Airblader/i3-original,Airblader/i3,stapelberg/i3,stapelberg/i3,Airblader/i3,i3/i3,Airblader/i3,stapelberg/i3,Airblader/i3-original,Airblader/i3,Airblader/i3-original,i3/i3,stapelberg/i3,Airblader/i3-original,Airblader/i3-original,i3/i3,i3/i3