Add production dependencies

node_modules/es5-ext/string/is-string.js

@@ -0,0 +1,13 @@
+"use strict";
+
+var objToString = Object.prototype.toString, id = objToString.call("");
+
+module.exports = function (value) {
+	return (
+		typeof value === "string" ||
+		(value &&
+			typeof value === "object" &&
+			(value instanceof String || objToString.call(value) === id)) ||
+		false
+	);
+};