Fix #79. Handle the since and until options in the authors output

Author: IonicaBizau

lib/index.js

@@ -526,7 +526,8 @@ GitStats.prototype.ansiCalendar = function (options, callback) {
  */
 GitStats.prototype.authors = function (options, callback) {
     var repo = new Gry(options.repo);
-    repo.exec("shortlog -s -n --all", function (err, stdout) {
+    debugger
+    repo.exec(`shortlog -s -n --all --since "${options.start.toString()}" --until "${options.end.toString()}"`, function (err, stdout) {
         if (err) { return callback(err); }
         var lines = stdout.split("\n");
         var pieData = stdout.split("\n").map(function (c) {