gbvendor/manifest.go: fix short url pointing to the right anchor

It was previously pointing to
https://github.com/FiloSottile/gvt#operlapping-dependencies

gbvendor/manifest.go

diff --git a/gbvendor/manifest.go b/gbvendor/manifest.go
index 0c3334b..d23b84e 100644
--- a/gbvendor/manifest.go
+++ b/gbvendor/manifest.go
@@ -181,7 +181,7 @@
 	for _, d := range deps {
 		if err := m.AddDependency(d); err == DepPresent {
 			log.Println("WARNING: overlapping dependency detected:", d.Importpath)
-			log.Println("The subpackage will be ignored to fix undefined behavior. See https://git.io/vwK4B")
+			log.Println("The subpackage will be ignored to fix undefined behavior. See https://git.io/vr8Mu")
 		} else if err != nil {
 			return nil, err
 		}