refactor(GuildChannel): change overwritePermisions to accept an array of overwrites

[NotSugden]

Please describe the changes this PR makes and why it should be merged:
This PR changes GuildChannel.overwritePermissions to accept an array of Permission Overwrites instead of an object, which previously would accept ChannelData, and the function just acting as an alias for GuildChannel.edit

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.