Update npm installation instructions

Author: dgraham

README.md

@@ -5,10 +5,8 @@ A Client Side Includes tag.
 
 ## Installation
 
-Available on [Bower](http://bower.io) as **include-fragment-element**.
-
 ```
-$ bower install include-fragment-element
+$ npm install --save include-fragment-element
 ```
 
 This component is built on the [Web Component](http://webcomponents.org/) stack. Specifically, it requires a feature called [Custom Elements](http://www.html5rocks.com/en/tutorials/webcomponents/customelements/). You'll need to use a polyfill to get this feature today. Either the [Polymer](http://www.polymer-project.org/) or [X-Tag](http://www.x-tags.org/) frameworks supply a polyfill, or you can install the standalone [CustomElements](https://github.com/webcomponents/webcomponentsjs) polyfill.
@@ -84,5 +82,5 @@ A proxy may attempt to fetch and replace the fragment if the request finishes be
 - Chrome
 - Firefox
 - Safari 9+
-- Internet Explorer 11+
+- Internet Explorer 11
 - Microsoft Edge