Rename write_hazardcurve_file to serialize_hazardcurve and fix the docstring.
Rename write_hazardcurve_file to serialize_hazardcurve and fix the docstring.


Former-commit-id: cdcf7ec1b1fb586eafba67cd1dc11ee9fb2cadfb
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine