gopls/go.mod: update golang.org/x/tools version for 0.4.2-pre1

Change-Id: I889adb95b6f9a4941127a340276e75e65c25d856
Reviewed-on: https://go-review.googlesource.com/c/tools/+/239563
Reviewed-by: Ian Cottrell <iancottrell@google.com>
diff --git a/gopls/go.mod b/gopls/go.mod
index 86f3e7b..a755e12 100644
--- a/gopls/go.mod
+++ b/gopls/go.mod
@@ -4,7 +4,7 @@
 
 require (
 	github.com/sergi/go-diff v1.1.0
-	golang.org/x/tools v0.0.0-20200515220128-d3bf790afa53
+	golang.org/x/tools v0.0.0-20200623225707-463a27d6af32
 	honnef.co/go/tools v0.0.1-2020.1.4
 	mvdan.cc/xurls/v2 v2.2.0
 )