Instead of checking for a non-windows OS, check for the presence of the node-pipe package before using it with zqd.

Non-windows platform require optional module node-pipe to ensure zqd is shutdown in the event brim getting SIGKILL'd. If for some reason node-pipe cannot be installed on a non-windows platform, we only find out about this when a user tries to startup a built copy of brim and the process fails when loading a non-existent node-pipe module.

Instead the either the build process or npm install should fail if node-pipe cannot be installed on a non-windows platform.