Change Details

Computing's master/slave metaphor is unnecessarily reminiscent of real slavery and not technically precise anyway. wmfdata-python uses "master" in a couple places: * as the primary Git branch. We should change this to `main` as long as it won't cause significant backwards-compatibility issues. * in the `spark` module, as Spark uses the term for the coordinator process (upstream is already [planning to remove the term](https://issues.apache.org/jira/browse/SPARK-32333) too). We can change all the references to it except in the actual PySpark call.

Computing's master/slave metaphor is unpleasantly reminiscent of real slavery and not technically precise anyway. wmfdata-python uses "master" in a couple places: * as the primary Git branch. We should change this to `main` as long as it won't cause significant backwards-compatibility issues. * in the `spark` module, as Spark uses the term for the coordinator process (upstream is already [planning to remove the term](https://issues.apache.org/jira/browse/SPARK-32333) too). We can change all the references to it except in the actual PySpark call.

Computing's master/slave metaphor is unnecessarilyunpleasantly reminiscent of real slavery and not technically precise anyway. wmfdata-python uses "master" in a couple places: * as the primary Git branch. We should change this to `main` as long as it won't cause significant backwards-compatibility issues. * in the `spark` module, as Spark uses the term for the coordinator process (upstream is already [planning to remove the term](https://issues.apache.org/jira/browse/SPARK-32333) too). We can change all the references to it except in the actual PySpark call.