Incorrect exception handling syntax in base plugin module

[jvarada]

nipype/nipype/pipeline/plugins/base.py

Line 148 in 9d793c1

except Exception, e:

Syntax is incompatible with python 3.

[oesteban]

Good catch!. It is also unnecessary since e is not used and the exception is retrieved right after with the exc_info. I'll be very happy to merge the PR when you send it.