Watchify events are not firing

Hi,

For severals files in my project, watchify is not working...

I tried and searched a lot but I didn't find a clue how to resolve this.

Everything is up to date. I'm using OSx with no virtual machine

Here is my gulp task :

```
gulp.task('browserify-watch', function () {
var bundler = watchify(browserify({ entries: 'app/main.js', debug: true }, watchify.args));
bundler.external(dependencies);
bundler.transform(babelify, { presets: ['es2015', 'react', 'stage-0'] });
bundler.on('update', rebundle);
return rebundle();

function rebundle() {
var start = Date.now();
return bundler.bundle()
.on('error', function(err) {
gutil.log(gutil.colors.red(err.toString()));
})
.on('end', function() {
gutil.log(gutil.colors.green('Finished rebundling in', (Date.now() - start) + 'ms.'));
})
.pipe(source('bundle.js'))
.pipe(buffer())
.pipe(sourcemaps.init({ loadMaps: true }))
.pipe(sourcemaps.write('.'))
.pipe(gulp.dest('public/js/'));
}
});
```