docs: use fulfillment instead of shipping in order totals example

[muzaffersenkal]

Description

Fixes #63

The example in the Order Capability documentation used "type": "shipping" in the totals array, but the schema defines the enum as:

• items_discount
• subtotal
• discount
• fulfillment
• tax
• fee
• total

Updated the example to use fulfillment to match the schema definition.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• Documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

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[surgarbear56-debug]

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[muzaffersenkal]

Hi @igrigorik , a reviewer on this PR seems to have publicly shared sensitive personal information. Could you please remove them as reviewer?