go/packages: fix doc typo
go/packages: fix doc typo

Fixes golang/go#34806

Change-Id: I21dea6def53030360890e888e29b33dfc9e4eed4
Reviewed-on: https://go-review.googlesource.com/c/tools/+/452578
Run-TryBot: Alan Donovan <7069e9552f9d110b0a0f326b96f22f63fb99dfc1@google.com>
Reviewed-by: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
gopls-CI: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools