Fix incorrect exception handling syntax

[akshayc11]

Python > 3.4 throws an incorrect syntax error if multiple exceptions being caught are not declared as tuples.

Traceback (most recent call last):
  File "steps/nnet3/chain/train.py", line 22, in <module>
    import libs.nnet3.report.log_parse as nnet3_log_parse
  File "steps/libs/nnet3/report/__init__.py", line 6, in <module>
    from . import log_parse
  File "steps/libs/nnet3/report/log_parse.py", line 535
    except KeyError, IndexError:
                   ^
SyntaxError: invalid syntax