Forward SIGTERM on bin wrapper to child process

Killing the parent process leaves the phantomjs binary child process
orphaned, unless we forward the signal to the child as well.

This commit handles SIGTERM only. It might perhaps be an idea to do
the same or similar with SIGINT as well.

bin/phantomjs

@@ -12,4 +12,9 @@ var args = process.argv.slice(2)
 var cp = spawn(binPath, args)
 cp.stdout.pipe(process.stdout)
 cp.stderr.pipe(process.stderr)
-cp.on('exit', process.exit)
+cp.on('exit', process.exit)
+
+process.on('SIGTERM', function() {
+  cp.kill('SIGTERM')
+  process.exit(1)
+})