[AIRFLOW-4044] The documentation of `query_params` in `BigQueryOperator` is wrong.  (#4876)
[AIRFLOW-4044] The documentation of `query_params` in `BigQueryOperator` is wrong.  (#4876)

* Updated the documentation of `query_params` in BigQueryOperator.

* Removed trailing whitespaces.

owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow