message: druid: use six.string_types instead of basestring
  Which is not available in python3
  Fix
diff: @@ -982,10 +982,10 @@ class DruidDatasource(Model, BaseDatasource):
  if op in ('in', 'not in'):
  eq = [
  types.replace("'", '').strip()
  - if isinstance(types, basestring)
  + if isinstance(types, string_types)
  else types
  for types in eq]
  - elif not isinstance(flt['val'], basestring):
  + elif not isinstance(flt['val'], string_types):
  eq = eq[0] if len(eq) > 0 else ''
  if col in self.num_cols:
  if op in ('in', 'not in'):
  