Fix Error: Cannot resolve module jquery

Following the instructions on the README was resulting in this error:

```
ERROR in ./bower_components/jquery.scrollTo/jquery.scrollTo.js
Module not found: Error: Cannot resolve module jquery in /tmp/tmp1456/webpack-intro/bower_components/jquery.scrollTo
 @ ./bower_components/jquery.scrollTo/jquery.scrollTo.js 14:8-35
```

Details:

```
fernando@fernando-E4300 /tmp/tmp1456 $ git clone https://github.com/davidgovea/webpack-intro.git
Cloning into 'webpack-intro'...
remote: Reusing existing pack: 36, done.
remote: Total 36 (delta 0), reused 0 (delta 0)
Unpacking objects: 100% (36/36), done.
Checking connectivity... done
fernando@fernando-E4300 /tmp/tmp1456 $ cd webpack-intro/
fernando@fernando-E4300 /tmp/tmp1456/webpack-intro $ npm install
(...)
hammerjs@1.0.6 node_modules/hammerjs

backbone@1.0.0 node_modules/backbone
└── underscore@1.5.2

webpack@0.11.18 node_modules/webpack
├── base64-encode@1.0.1
├── tapable@0.1.3
├── clone@0.1.11
├── async@0.2.9
├── mkdirp@0.3.5
├── enhanced-resolve@0.5.15
├── esprima@1.0.4
├── optimist@0.6.0 (wordwrap@0.0.2, minimist@0.0.5)
├── webpack-core@0.2.12 (source-map@0.1.31)
├── uglify-js@2.4.9 (uglify-to-browserify@1.0.1, optimist@0.3.7, source-map@0.1.31)
└── node-libs-browser@0.1.2 (console-browserify@0.1.6, zlib-browserify@0.0.1, vm-browserify@0.0.1, crypto-browserify@0.2.1, buffer-browserify@0.0.4, http-browserify@0.1.6)
fernando@fernando-E4300 /tmp/tmp1456/webpack-intro $ bower install
bower modernizr#~2.6.2          cached git://github.com/Modernizr/Modernizr.git#2.6.3
bower modernizr#~2.6.2        validate 2.6.3 against git://github.com/Modernizr/Modernizr.git#~2.6.2
bower jquery.scrollTo#~1.4.6    cached git://github.com/flesler/jquery.scrollTo.git#1.4.9
bower jquery.scrollTo#~1.4.6  validate 1.4.9 against git://github.com/flesler/jquery.scrollTo.git#~1.4.6
bower jquery#~2.0.3             cached git://github.com/components/jquery.git#2.0.3
bower jquery#~2.0.3           validate 2.0.3 against git://github.com/components/jquery.git#~2.0.3
bower jquery#>=1.8              cached git://github.com/components/jquery.git#2.0.3
bower jquery#>=1.8            validate 2.0.3 against git://github.com/components/jquery.git#>=1.8
bower jquery.scrollTo#~1.4.6   install jquery.scrollTo#1.4.9
bower jquery#~2.0.3            install jquery#2.0.3
bower modernizr#~2.6.2         install modernizr#2.6.3

jquery.scrollTo#1.4.9 bower_components/jquery.scrollTo
└── jquery#2.0.3

jquery#2.0.3 bower_components/jquery

modernizr#2.6.3 bower_components/modernizr
fernando@fernando-E4300 /tmp/tmp1456/webpack-intro $ make
Hash: b4335aa03db5af5e678e
Version: webpack 0.11.18
Time: 1795ms
      Asset    Size  Chunks             Chunk Names
  bundle.js  417618       0  [emitted]  main       
1.bundle.js   42731       1  [emitted]             
   [0] ./entry.js 1237 {0} [built]
   [1] ./bower_components/modernizr/modernizr.js 50144 {0} [built]
   [2] ./bower_components/jquery/jquery.js 242142 {0} [built]
   [3] ./bower_components/jquery.scrollTo/jquery.scrollTo.js 5353 {0} [built] [1 error]
   [4] (webpack)/buildin/module.js 251 {0} [built]
   [5] ./~/backbone/backbone.js 59498 {0} [built]
   [6] ./~/hammerjs/hammer.js 41337 {1} [built]
   [7] ./~/backbone/~/underscore/underscore.js 43566 {0} [built]

ERROR in ./bower_components/jquery.scrollTo/jquery.scrollTo.js
Module not found: Error: Cannot resolve module jquery in /tmp/tmp1456/webpack-intro/bower_components/jquery.scrollTo
 @ ./bower_components/jquery.scrollTo/jquery.scrollTo.js 14:8-35
```