Bump to v4.0.0.

add.js

@@ -0,0 +1,26 @@
+/**
+ * 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;
+}
+
+export default add;