Bump gotuf

Signed-off-by: Diogo Monica <diogo@docker.com>

Godeps/Godeps.json

@@ -63,7 +63,7 @@
 		},
 		{
 			"ImportPath": "github.com/endophage/gotuf",
-			"Rev": "a8a23ab6e67bd0e9fbaf563aabd9e6ee7ea344d2"
+			"Rev": "9640c9b3f2ff0ba75baf7d1a57632e16cb78d5e6"
 		},
 		{
 			"ImportPath": "github.com/go-sql-driver/mysql",

Godeps/_workspace/src/github.com/endophage/gotuf/signed/verify.go

@@ -52,7 +52,13 @@ func VerifyRoot(s *data.Signed, minVersion int, keys map[string]data.PublicKey)
 			continue
 		}
 
-		if err := verifier.Verify(keys[sig.KeyID], sig.Signature, msg); err != nil {
+		key, ok := keys[sig.KeyID]
+		if !ok {
+			logrus.Debugf("continuing b/c signing key isn't present in keys: %s\n", sig.KeyID)
+			continue
+		}
+
+		if err := verifier.Verify(key, sig.Signature, msg); err != nil {
 			logrus.Debugf("continuing b/c signature was invalid\n")
 			continue
 		}