Updated the parse_args in the MassWeightedStdDistProtocol to look for…

… selection_string setting keyword instead of selection.

pybilt/bilayer_analyzer/analysis_protocols.py

@@ -1462,7 +1462,7 @@ def _parse_str_to_dict(self, args):
                     arg_dict['n_bins'] = int(arg_arg)
                     read_sel_string = False
                     n_bins_arg = True
-                elif arg_key == 'selection':
+                elif arg_key == 'selection_string':
                     selection_words = [args[j] for j in range(i + 1, nargs) if
                                        (args[j] not in self._valid_settings)]
                     i += len(selection_words)