Listing messages accepts conversationId instead of contactId

[lorenzosani]

https://github.com/messagebird/messagebird-nodejs/blob/2d8b7de16c6c4c24829bc009dfa29c59a68ab189/types/index.d.ts#L240

When calling MessageBird.conversations.listMessages, the call doesn't work if a contactId is passed, but works when the conversationId is passed. I believe this behaviour is correct, but the parameter name should be changed from contactId to conversationId if this is the case