fix: image -> image/x-icon

[poyoho]

Description

thanks @lukeed

ico is officially the image/vnd.microsoft.icon mime type and also has had image/x-icon recognized, but both are vendor-specific and/or experimental so mrmime does not include them. The image or image/icon solutions are all userland names and not officially true

Additional context

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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