After updating to ST4 (build 4113), the builder does not launch the PDF viewer (Skim) any more. (MacOS 10.14.6 Mojave, Skim 1.6.4). I tried changing the viewer commands in LaTeXTools.sublime-settings, but it seems that viewer-related commands are simply ignored. latexmk etc. seem to work fine, as does \cite resolution etc., and I can use the settings file to toggle output of logs in the console, for example.