Fix GetResult call on async method in an async context.

Created by: GreemDev

Summary

Changes the DSharpPlus.Rest.DiscordRestClient to use await where it can, rather than GetAwaiter().GetResult() in an async context.

Details

In the current code, this line blocks. So instead of doing that, it should be awaited to avoid deadlocking.

Changes proposed

• await this line.