gopls: update go.mod for gopls/v0.3.1-pre1

Change-Id: I53b1a80f83ff3a32c277f9fea0fa92c86bf5d8b2
Reviewed-on: https://go-review.googlesource.com/c/tools/+/217718
Reviewed-by: Robert Findley <rfindley@google.com>
diff --git a/gopls/go.mod b/gopls/go.mod
index 42e3817..b5695d0 100644
--- a/gopls/go.mod
+++ b/gopls/go.mod
@@ -5,7 +5,7 @@
 require (
 	github.com/sergi/go-diff v1.0.0
 	github.com/stretchr/testify v1.4.0 // indirect
-	golang.org/x/tools v0.0.0-20200130224948-02f1738cbe39
+	golang.org/x/tools v0.0.0-20200204151227-34c67990bfe7
 	honnef.co/go/tools v0.0.1-2019.2.3
 	mvdan.cc/xurls/v2 v2.1.0
 )