Bump to v4.0.0.

add.js

@@ -0,0 +1,32 @@
+define([], function() {
+
+  /** Used as a safe reference for `undefined` in pre-ES5 environments. */
+  var undefined;
+
+  /**
+   * Adds two numbers.
+   *
+   * @static
+   * @memberOf _
+   * @category Math
+   * @param {number} augend The first number in an addition.
+   * @param {number} addend The second number in an addition.
+   * @returns {number} Returns the total.
+   * @example
+   *
+   * _.add(6, 4);
+   * // => 10
+   */
+  function add(augend, addend) {
+    var result;
+    if (augend !== undefined) {
+      result = augend;
+    }
+    if (addend !== undefined) {
+      result = result === undefined ? addend : (result + addend);
+    }
+    return result;
+  }
+
+  return add;
+});