gopls: update x/tools for next pre-release

Not bothering to update the hardcoded version string at this point.

Change-Id: If9b821c0d0ac6eb64571343beffb51da409c30d3
Reviewed-on: https://go-review.googlesource.com/c/tools/+/217089
Reviewed-by: Michael Matloob <matloob@golang.org>

gopls/go.mod

@@ -5,7 +5,7 @@ go 1.11
 require (
 	github.com/sergi/go-diff v1.0.0
 	github.com/stretchr/testify v1.4.0 // indirect
-	golang.org/x/tools v0.0.0-20200128221035-c00a2daf0567
+	golang.org/x/tools v0.0.0-20200130224948-02f1738cbe39
 	honnef.co/go/tools v0.0.1-2019.2.3
 	mvdan.cc/xurls/v2 v2.1.0
 )