package.json: sync gopls settings (gopls@v0.15.0-pre.1)

Change-Id: If55c3a89cd28fd7ea7b7c022b98ec9b6c7b3fec1
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/554060
Commit-Queue: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>

Author: hyangah