Fix typo

Julien LepillerMon Jan 27 14:47:30+0100 2020

477b656

Fix typo

activitystreams/ontology.scm

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(define as:deleted
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  (make-as-property
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    "deleted" "Tombostone" date?
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    "deleted" "Tombstone" date?
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    #:functional? #t
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    #:comment
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    "On a Tombstone object, the deleted property is a timestamp for when the