Make vanity metadata parsing more lenient

Imports golang/go@5b085482 and golang/go@81a4bbff

Closes #31
diff --git a/gbvendor/discovery.go b/gbvendor/discovery.go
index f504200..45da7ae 100644
--- a/gbvendor/discovery.go
+++ b/gbvendor/discovery.go
@@ -38,9 +38,9 @@
 	d.Strict = false
 	var t xml.Token
 	for {
-		t, err = d.Token()
+		t, err = d.RawToken()
 		if err != nil {
-			if err == io.EOF {
+			if err == io.EOF || len(imports) > 0 {
 				err = nil
 			}
 			return