Modify source map to move everything down by five lines

blah.js

var DOCBLOCK_LINES = 5;
var first = new sourceMap.SourceMapConsumer(input);

var generator = new sourceMap.SourceMapGenerator({
  file: first.file,
});
first.eachMapping(function(mapping) {
  generator.addMapping({
    generated: {
      column: mapping.generatedColumn,
      line: mapping.generatedLine + DOCBLOCK_LINES,
    },
    original: {
      column: mapping.originalColumn,
      line: mapping.originalLine,
    },
    source: mapping.source
  });
});
first.sources.forEach(function(sourceFile) {
  generator.setSourceContent(sourceFile, first.sourceContentFor(sourceFile));
});
console.log(generator.toString());