py 2 and 3

http://python3porting.com/noconv.html#handling-exceptions

this is the first error i get when i try to start th eviewer from python 3
using the two-line from https://github.com/IfcOpenShell/IfcOpenShell/commit/1d1fb6d27a5bb1f221aed4dc290c1dc99a324e0f#commitcomment-17161165

src/ifcopenshell-python/ifcopenshell/geom/app.py

@@ -333,7 +333,7 @@ class application(QtGui.QApplication):
                             if type_psets is None: continue
                             for propset in type_psets:
                                 propsets.append(process_pset(propset))
-                except Exception, e:
+                except Exception as e:
                     import traceback
                     print("failed to load properties: {}".format(e))
                     traceback.print_exc()