internal/lsp/cmd: use x/tools/gopls as the gopls bug prefix
internal/lsp/cmd: use x/tools/gopls as the gopls bug prefix

"x/tools/gopls" appears to be the currently used prefix for gopls
issues. Make "gopls bug" use this prefix instead of just "gopls" to
avoid needing to edit titles before/after submitting.

Change-Id: I7244aa5539332cc361870f49ae4f27b2a2441571
Reviewed-on: https://go-review.googlesource.com/c/tools/+/209964
Reviewed-by: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>
Run-TryBot: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

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