Missing final CRLF after progress reporter finishes

[bkimminich]

A small cosmetic bug that happens when using reporter: ['html', 'progress']:

The clear-text reporter does an initial CRLF on the sysout using this helper method:

private writeLine(output?: string) {
    this.out.write(`${output || ''}\n`);
  }

That's why it doesn't happen when using clear-text together with progress:

[nicojs]

I think the easiest way to fix this is to add this method to add this method to the ProgressReporter

onAllMutantsTested(): void { 
   console.log();
}

Not sure if this would help in all situations though.

[nicojs]

Merged into the master brache, will be released later this week.