Added missing softsign import (#5521)

theano/tensor/nnet/__init__.py

@@ -18,7 +18,7 @@ from .nnet import (
     logsoftmax, logsoftmax_op, prepend_0_to_each_row, prepend_1_to_each_row,
     prepend_scalar_to_each_row, relu, softmax, softmax_grad, softmax_graph,
     softmax_op, softmax_simplifier, softmax_with_bias, elu,
-    confusion_matrix)
+    confusion_matrix, softsign)
 from . import opt
 from .conv import ConvOp
 from .Conv3D import *