update watchify recipe to generate and read browserify sourcemaps

docs/recipes/fast-browserify-builds-with-watchify.md

@@ -7,34 +7,40 @@ That's why [substack](http://github.com/substack) wrote [watchify](http://github
 Watchify doesn't have a gulp plugin, but it doesn't need one either: you can use [vinyl-source-stream](http://github.com/hughsk/vinyl-source-stream) to pipe the bundle stream into your gulp pipeline.
 
 ``` javascript
+'use strict';
+
+var watchify = require('watchify');
+var browserify = require('browserify');
 var gulp = require('gulp');
-var gutil = require('gulp-util');
-var sourcemaps = require('gulp-sourcemaps');
 var source = require('vinyl-source-stream');
 var buffer = require('vinyl-buffer');
-var watchify = require('watchify');
-var browserify = require('browserify');
+var gutil = require('gulp-util');
+var sourcemaps = require('gulp-sourcemaps');
+var assign = require('lodash.assign');
 
-var bundler = watchify(browserify(watchify.args));
-// add the file to bundle
-bundler.add('./src/index.js');
-// add any other browserify options or transforms here
-bundler.transform('brfs');
+// add custom browserify options here
+var customOpts = {
+  entries: ['./src/index.js'],
+  debug: true
+};
+var opts = assign(customOpts, watchify.args);
+var b = watchify(browserify(opts));
 
 gulp.task('js', bundle); // so you can run `gulp js` to build the file
-bundler.on('update', bundle); // on any dep update, runs the bundler
-bundler.on('log', gutil.log); // output build logs to terminal
+b.on('update', bundle); // on any dep update, runs the bundler
+b.on('log', gutil.log); // output build logs to terminal
 
 function bundle() {
-  return bundler.bundle()
+  return b.bundle()
     // log errors if they happen
     .on('error', gutil.log.bind(gutil, 'Browserify Error'))
     .pipe(source('bundle.js'))
+    // optional, remove if you don't need to buffer file contents
+    .pipe(buffer())
     // optional, remove if you dont want sourcemaps
-      .pipe(buffer())
-      .pipe(sourcemaps.init({loadMaps: true})) // loads map from browserify file
-      .pipe(sourcemaps.write('./')) // writes .map file
-    //
+    .pipe(sourcemaps.init({loadMaps: true})) // loads map from browserify file
+       // Add transformation tasks to the pipeline here.
+    .pipe(sourcemaps.write('./')) // writes .map file
     .pipe(gulp.dest('./dist'));
 }
 ```