print_model_weights does not work for Logistic Regression models without intercepts.

[desilinguist]

Here's the error I get:

Traceback (most recent call last):
  File "/Users/nmadnani/anaconda/envs/garbage/bin/print_model_weights", line 6, in <module>
    sys.exit(main())
  File "/Users/nmadnani/anaconda/envs/garbage/lib/python3.4/site-packages/skll/utilities/print_model_weights.py", line 55, in main
    (weights, intercept) = learner.model_params
  File "/Users/nmadnani/anaconda/envs/garbage/lib/python3.4/site-packages/skll/learner.py", line 712, in model_params
    intercept = dict(zip(label_list, self.model.intercept_))
TypeError: zip argument #2 must support iteration

[dan-blanchard]

Fixed by #251.