Bugfix in vanillalstm serialization
Bugfix in vanillalstm serialization

vanillalstm didn't save `hid` which causes errors when loading a saved model. Couldn't test this but should be fine.

Former-commit-id: 39fc3318b3f71324e1eeb9e2dfd1c12b640767ef
shuheik/dynet,danielhers/dynet,shuheik/dynet,clab/dynet,clab/dynet,shuheik/dynet,danielhers/dynet,shuheik/dynet,clab/dynet,danielhers/dynet,danielhers/dynet,shuheik/dynet,clab/cnn,clab/dynet,clab/dynet,clab/cnn,shuheik/dynet,xunzhang/dynet,danielhers/dynet,chunyang-wen/dynet,chunyang-wen/dynet,chunyang-wen/dynet,xunzhang/dynet,xunzhang/dynet,danielhers/dynet,clab/cnn,danielhers/dynet,xunzhang/dynet,shuheik/dynet,clab/dynet,clab/dynet,chunyang-wen/dynet