Fixed #31.

Author: pluma

dist/arango.all.js

@@ -1787,9 +1787,15 @@ module.exports = function promisify(callback) {
   var promise = new Promise(function (resolve, reject) {
     callback = function (err, res) {
       if (err) reject(err);else resolve(res);
-      if (cb) cb(err, res);
     };
   });
+  if (cb) {
+    promise.then(function (result) {
+      return cb(null, result);
+    }, function (reason) {
+      return cb(reason);
+    });
+  }
   return { callback: callback, promise: promise };
 };
 },{}],11:[function(require,module,exports){

dist/arango.all.min.js

@@ -1787,9 +1787,15 @@ module.exports = function promisify(callback) {
   var promise = new Promise(function (resolve, reject) {
     callback = function (err, res) {
       if (err) reject(err);else resolve(res);
-      if (cb) cb(err, res);
     };
   });
+  if (cb) {
+    promise.then(function (result) {
+      return cb(null, result);
+    }, function (reason) {
+      return cb(reason);
+    });
+  }
   return { callback: callback, promise: promise };
 };
 },{}],11:[function(require,module,exports){

dist/arango.js

@@ -7,8 +7,14 @@ module.exports = function promisify(callback) {
   var promise = new Promise(function (resolve, reject) {
     callback = function (err, res) {
       if (err) reject(err);else resolve(res);
-      if (cb) cb(err, res);
     };
   });
+  if (cb) {
+    promise.then(function (result) {
+      return cb(null, result);
+    }, function (reason) {
+      return cb(reason);
+    });
+  }
   return { callback: callback, promise: promise };
 };

dist/arango.min.js

@@ -8,8 +8,13 @@ module.exports = function promisify(callback) {
     callback = function (err, res) {
       if (err) reject(err);
       else resolve(res);
-      if (cb) cb(err, res);
     };
   });
+  if (cb) {
+    promise.then(
+      result => cb(null, result),
+      reason => cb(reason)
+    );
+  }
   return {callback, promise};
 };