Compile files from multiple separate directories in a single output

Question

For reasons beyond my control, I have my source code in separate and unrelated directories. Like this:

diretorioPai
    foo
        serverSideJS
        clientSideJS
    bar
        serverSideJS
        clientSideJS

I set up the Browserify (with watchify) to use multiple inputs and have only one output. My problem is that the watchify only accompanies a directory - The first in the list of entries. It does not detect changes in the second directory (nor of others more that I add). I have found that no errors are triggered.

Those are the relevant parts of my gulpfile:

gulp.task('js', function () {
    var dir1 = '/diretorioPai/foo/clientSideJS';
    var dir2 = '/diretorioPai/bar/clientSideJS'

    var opts = {
        entries: [dir1, dir2]
    }
    opts = xtend(opts, watchify.args);

    var bundler = browserify(opts);
    bundler = watchify(bundler);

    bundler.on('update', function (file) {
        gutil.log('Arquivo ' + file + ' alterado.');
        rebundle();
    });

    function rebundle () {
        return bundler
            .bundle()
            .on('error', function (e) {
                gutil.log('Error durante a compilação. : ' + e);
            })
            .on('finish', function (e) {
                gutil.log('Pronto.');
            })
            .pipe(source('app.js'))
            .pipe(gulp.dest('/diretorioDeSaida/JS'));
    }
    return rebundle();
});

How do I make for the Browserify, or at least the Browserify, track files in several directories and compile what you find in one file only?