By default, Plumber is not piped in your scripts task but it’s already included in the packages loaded via npm.
You can replace your scripts task with the following
var onError = function (err) {
  console.log(err.toString());
   this.emit('end');
};
gulp.task('scripts', ['jshint'], function() {
  var merged = merge();
  manifest.forEachDependency('js', function(dep) {
    merged.add(
      gulp.src(dep.globs, {base: 'scripts'})
        .pipe(plumber({ errorHandler: onError }))
        .pipe(jsTasks(dep.name))
    );
  });
  return merged
    .pipe(writeToManifest('scripts'));
});