Nostrum diverges from nip46 specs in sign_event

[riccardobl]

in sign_event specs
sign_event [<{kind, content, tags, created_at}>]

nip46 specifies params to be

positional array of string parameters.

this points to the correct way to encode the event being [JSON.stringify({kind,content,tags,created_at})]
nostrum (built from master branch) expects it to be passed as json object [{kind,content,tags,created_at}] instead