Fix indentation for code examples in package.json doc

Fixes the following rendering issues on https://www.npmjs.org/doc/files/package.json.html

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![package json 2014-02-20 13-35-44](https://f.cloud.github.com/assets/65633/2223834/3b9d3546-9a77-11e3-953c-e0c0096fad57.png)

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![package json 2014-02-20 13-35-32](https://f.cloud.github.com/assets/65633/2223835/3b9d68b8-9a77-11e3-8e4f-97a7b38da7e5.png)

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