Only reset sessionID when close code is 1000 or 4006

[Deivu]

Please describe the changes this PR makes and why it should be merged:
This resolves #3191 where in resumed never fires.

I don't think 1001 should be included on resetting the sessionID based on Line 372 & 373 of https://github.com/discordjs/discord.js/blob/master/src/client/websocket/WebSocketShard.js

Using latest master with this modification fixed my issue entirely, refer to screenshot below.
https://media.discordapp.net/attachments/222197033908436994/568036331452891146/unknown.png?width=297&height=211

Status

• Code changes have been tested against the Discord API, or there are no code changes
• I know how to update typings and have done so, or typings don't need updating

Semantic versioning classification:

• This PR changes the library's interface (methods or parameters added)
  • This PR includes breaking changes (methods removed or renamed, parameters moved or removed)
• This PR only includes non-code changes, like changes to documentation, README, etc.

[amishshah]

Thanks very much for your PR!

According to this flowchart, the session only remains valid if the close code is not 1000 or 4006 -- looks like we're using some old code from when this may have not been the case.

Could you update the PR to invalidate the session ID if the code is one of these two?

Thanks!

[Deivu]

Done updating the pr