docs(query): correct function signature for .mod() helper

Fix #1806

Author: vkarpov15

lib/query.js

@@ -531,17 +531,51 @@ Query.prototype.slice = function() {
  */
 
 /**
- * Specifies a `$mod` condition
+ * Specifies a `$mod` condition, filters documents for documents whose
+ * `path` property is a number that is equal to `remainder` modulo `divisor`.
+ *
+ * ####Example
+ *
+ *     // All find products whose inventory is odd
+ *     Product.find().mod('inventory', [2, 1]);
+ *     Product.find().where('inventory').mod([2, 1]);
+ *     // This syntax is a little strange, but supported.
+ *     Product.find().where('inventory').mod(2, 1);
  *
  * @method mod
  * @memberOf Query
  * @param {String} [path]
- * @param {Number} val
+ * @param {Array} val must be of length 2, first element is `divisor`, 2nd element is `remainder`.
  * @return {Query} this
  * @see $mod http://docs.mongodb.org/manual/reference/operator/mod/
  * @api public
  */
 
+Query.prototype.mod = function() {
+  var val;
+  var path;
+
+  if (arguments.length === 1) {
+    this._ensurePath('mod');
+    val = arguments[0];
+    path = this._path;
+  } else if (arguments.length === 2 && !Array.isArray(arguments[1])) {
+    this._ensurePath('mod');
+    val = slice(arguments);
+    path = this._path;
+  } else if (arguments.length === 3) {
+    val = slice(arguments, 1);
+    path = arguments[0];
+  } else {
+    val = arguments[1];
+    path = arguments[0];
+  }
+
+  var conds = this._conditions[path] || (this._conditions[path] = {});
+  conds.$mod = val;
+  return this;
+};
+
 /**
  * Specifies an `$exists` condition
  *