Return a version of the source code with PEP 8 violations fixed.

def fix(self):
        """Return a version of the source code with PEP 8 violations fixed."""
        pep8_options = {
            'ignore': self.options.ignore,
            'select': self.options.select,
            'max_line_length': self.options.max_line_length,
            'hang_closing': self.options.hang_closing,
        }
        results = _execute_pep8(pep8_options, self.source)

        if self.options.verbose:
            progress = {}
            for r in results:
                if r['id'] not in progress:
                    progress[r['id']] = set()
                progress[r['id']].add(r['line'])
            print('--->  {n} issue(s) to fix {progress}'.format(
                n=len(results), progress=progress), file=sys.stderr)

        if self.options.line_range:
            start, end = self.options.line_range
            results = [r for r in results
                       if start <= r['line'] <= end]

        self._fix_source(filter_results(source=''.join(self.source),
                                        results=results,
                                        aggressive=self.options.aggressive))

        if self.options.line_range:
            # If number of lines has changed then change line_range.
            count = sum(sline.count('\n')
                        for sline in self.source[start - 1:end])
            self.options.line_range[1] = start + count - 1

        return ''.join(self.source)