bugfix in matmul signature (#565)
bugfix in matmul signature (#565)



Former-commit-id: fcd2ef6bfa9ecb4e891d37883ba68f8568742dd5
danielhers/dynet,shuheik/dynet,xunzhang/dynet,shuheik/dynet,xunzhang/dynet,clab/dynet,danielhers/dynet,danielhers/dynet,danielhers/dynet,clab/cnn,clab/dynet,clab/cnn,shuheik/dynet,xunzhang/dynet,danielhers/dynet,clab/cnn,chunyang-wen/dynet,xunzhang/dynet,clab/dynet,shuheik/dynet,shuheik/dynet,chunyang-wen/dynet,chunyang-wen/dynet,clab/dynet,clab/dynet,shuheik/dynet,clab/dynet,danielhers/dynet,shuheik/dynet,clab/dynet,chunyang-wen/dynet,danielhers/dynet