also fix the old style exception catching syntax

[cdsontag]

Also fix the old style exception catching syntax.

And fix an incorrect indent during a whitespace change in the last PR, #36.

See syntax errors in this Py3 run log:

• http://plglitch.stsci.edu:8080/jwst/test/reports/logs/pandeia_cp_of_master_2018-12-21-15:36:38.main