Use SGD for stop -token layer

train.py

@@ -361,7 +361,8 @@ def main(args):
                      c.r)
 
     optimizer = optim.Adam(model.parameters(), lr=c.lr)
-    optimizer_st = optim.Adam(model.decoder.stopnet.parameters(), lr=c.lr)
+    optimizer_st = optim.SGD(model.decoder.stopnet.parameters(), lr=0.01,
+                             momentum=0.9, nesterov=True)
 
     criterion = L1LossMasked()
     criterion_st = nn.BCELoss()