text: Title: param col_names for indicators with one resulting column
  Body: Some indicators return multiple columns, then it is possible to rename the returned columns with `col_names` but for indicators with just one column this is not working e.g. for kind wma
  
  The renaming happens at https://github.com/twopirllc/pandas-ta/blob/b2f2cc83a16376c1eb0a11aebed52186d7eab121/pandas_ta/core.py#L406
  but i cant seee why it should not work for indicators with just one resulting column