gopls: update go.mod for gopls/v0.5.1-pre1

Change-Id: I96b4196bb3fab56067b1b92c3ba2f2470d461d77
Reviewed-on: https://go-review.googlesource.com/c/tools/+/257597
Trust: Rebecca Stambler <rstambler@golang.org>
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

Author: stamblerre

gopls/go.mod

@@ -4,7 +4,7 @@ go 1.12
 
 require (
 	github.com/sergi/go-diff v1.1.0
-	golang.org/x/tools v0.0.0-20200914163123-ea50a3c84940
+	golang.org/x/tools v0.0.0-20200925151336-0322e45e3e6c
 	golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1
 	honnef.co/go/tools v0.0.1-2020.1.5
 	mvdan.cc/gofumpt v0.0.0-20200802201014-ab5a8192947d