deflake TestNavigate

For some reason, this test fails about half the time on Travis, but I
can't get it to fail even after stress-testing hundreds of concurrent
runs.

It might be because Travis is on a much older version of Chrome. We'll
fix that soon, by having chromedp select a specific version of Chrome.

For now, make it more conservative, not assuming that a Location after a
Navigate isn't racy.

nav_test.go

@@ -23,8 +23,8 @@ func TestNavigate(t *testing.T) {
 
 	var urlstr string
 	if err := Run(ctx,
-		Location(&urlstr),
 		WaitVisible(`#icon-brankas`, ByID),
+		Location(&urlstr),
 	); err != nil {
 		t.Fatal(err)
 	}