README: fix typo

Author: piperchester

README.md

@@ -29,7 +29,7 @@ Polymer 2.0 is released, and will be the future focus of Polymer development goi
 
 ## Overview
 
-Polymer is a lightweight library built on top of the web standards-based [Web Components](http://webcomponents.org/) API's, and makes it easier to build your very own custom HTML elements. Creating reusable custom elements - and using elements built by others - can make building complex web applications easier and more efficient. By being based on the Web Components API's built in the browser (or [polyfilled](https://github.com/webcomponents/webcomponentsjs) where needed), Polymer elements are interoperable at the browser level, and can be used with other frameworks or libraries that work with modern browsers.
+Polymer is a lightweight library built on top of the web standards-based [Web Components](http://webcomponents.org/) APIs, and makes it easier to build your very own custom HTML elements. Creating reusable custom elements - and using elements built by others - can make building complex web applications easier and more efficient. By being based on the Web Components API's built in the browser (or [polyfilled](https://github.com/webcomponents/webcomponentsjs) where needed), Polymer elements are interoperable at the browser level, and can be used with other frameworks or libraries that work with modern browsers.
 
 Among many ways to leverage custom elements, they can be particularly useful for building reusable UI components. Instead of continually re-building a specific navigation bar or button in different frameworks and for different projects, you can define this element once using Polymer, and then reuse it throughout your project or in any future project.