When not giving `--genome_size` for long reads, message goes to log and not console

[fmalmeida]

When running a samplesheet that has longreads assemblies, if one forget to give the --genome_size parameter, the pipeline exits without showing the error message in the console. The message appears only in the .nextflow.log

Problem is in file https://github.com/fmalmeida/MpGAP/blob/master/nf_functions/writeCSV.nf

Instead of println should be log.error and instead of exit 1 should be System.exit(1).

[fmalmeida]

This was a problem in master but in the dev branch, the log.error function is already being used and thus, it is working properly and this is irrelevant.