The dim parameter is new and will be in the next release. The docs are fixed too. Here’s what it says in master, if you build from source:
In [5]: ?torch.nn.functional.log_softmax
Signature: torch.nn.functional.log_softmax(input, dim=None, _stacklevel=3)
Docstring:
Applies a softmax followed by a logarithm.

While mathematically equivalent to log(softmax(x)), doing these two
operations separately is slower, and numerically unstable. This function
uses an alternative formulation to compute the output and gradient correctly.

See :class:`~torch.nn.LogSoftmax` for more details.

Arguments:
    input (Variable): input
    dim (int): A dimension along which log_softmax will be computed.
File:      /data/users/sgross/pytorch/torch/nn/functional.py
Type:      function

You can always use docs.pytorch.org 87