gopls: update go.mod file for v0.4.2

Change-Id: Ibfb231a2d2f11b1fa98e2d7eec7776763d544756
Reviewed-on: https://go-review.googlesource.com/c/tools/+/240507
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

gopls/go.mod

@@ -4,7 +4,7 @@ go 1.13
 
 require (
 	github.com/sergi/go-diff v1.1.0
-	golang.org/x/tools v0.0.0-20200630154708-24ca011bb20f
+	golang.org/x/tools v0.0.0-20200701133321-6ddc6be4d35f
 	honnef.co/go/tools v0.0.1-2020.1.4
 	mvdan.cc/xurls/v2 v2.2.0
 )