Fix error in quick-start example

Following [Pylearn2's quick-start example] (http://deeplearning.net/software/pylearn2/tutorial/index.html#tutorial leads) to the following error when attempting to visualize RBM weights with the show_weights.py script.  
```
Traceback (most recent call last):
  File "../../show_weights.py", line 52, in <module>
    show_weights(args.path, args.rescale, args.border, args.out)
  File "../../show_weights.py", line 28, in show_weights
    border=border)
  File "/home/mmay/Downloads/Installs/pylearn2/pylearn2/gui/get_weights_report.py", line 142, in get_weights_report
    weights_view = dataset.get_weights_view(W)
AttributeError: 'str' object has no attribute 'get_weights_view'
```
A simple fix described [here] (http://goo.gl/pczYTx) resolves the issue.