Guild.fetchAuditLogs corresponding API endpoint does not accept the documented "after" parameter

[monbrey]

Please describe the problem you are having in as much detail as possible:
Guild.fetchAuditLogs() is documented as and coded to accept options.after, however the API endpoint does not accept this parameter.
https://discord.js.org/#/docs/main/stable/class/Guild?scrollTo=fetchAuditLogs
https://github.com/discordjs/discord.js/blob/master/src/structures/Guild.js#L569
https://discordapp.com/developers/docs/resources/audit-log#get-guild-audit-log-query-string-parameters

Include a reproducible code sample here, if possible:

client.guilds.get("guild_id_here").fetchAuditLogs({limit: "2"})
// Will correctly return two logs. Get the Snowflake of the older log
client.guilds.get("same_guild_id_here").fetchAuditLogs({after: "older_audit_log_id"})
// Expected behaviour would be to return 1 or 2 logs, depending on if `after` was inclusive. Since it doesnt exist at all, it returns the default 50

Further details:

• discord.js version: Tested on stable by me, master by someone else
• Node.js version: v10.15.0
• Operating system: Windows 10
• Priority this issue should have – please be realistic and elaborate if possible: Fixing - low. Changing the documentation to not be misleading - maybe medium since its easy to do, will probably PR it myself

• I have also tested the issue on latest master, commit hash: I haven't, but the offending code is still there

[monbrey]

#3142