Field name missing

[boriscosic]

field_name is missing to correctly describe the field that raised an error. For example:

source_row_index,violating_table,violation_key,violation_type,violation_severity,violation_comment
2,sonde_data.csv,,required,error,date_in value is required but was empty,date_in

This causes the validation checker, which uses csv-parse to bail with incorrect column count. The column headers are appended here https://github.com/tesera/datapackage-validator-awslambda/blob/master/fkeychecks.sh#L35.