gopls: update go.mod for gopls/v0.5.0-pre3

Change-Id: I9811439e567e0ac1a7cc0a6c018d06076fed2b17
Reviewed-on: https://go-review.googlesource.com/c/tools/+/254798
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Rebecca Stambler <rstambler@golang.org>
Trust: Heschi Kreinick <heschi@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>

gopls/go.mod

@@ -4,7 +4,7 @@ go 1.13
 
 require (
 	github.com/sergi/go-diff v1.1.0
-	golang.org/x/tools v0.0.0-20200913034212-796b347e00a4
+	golang.org/x/tools v0.0.0-20200914163123-ea50a3c84940
 	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