Update installation.md

fix wording

examples/docs/en-US/installation.md

@@ -1,7 +1,7 @@
 ## Installation
 
 ### npm
-Installing with npm is recommended, for it works seamlessly with [webpack](https://webpack.js.org/).
+Installing with npm is recommended and it works seamlessly with [webpack](https://webpack.js.org/).
 
 ```shell
 npm i element-ui -D
@@ -50,4 +50,4 @@ If you are using CDN, a hello-world page is easy with Element. [Online Demo](htt
   </script>
 </html>
 ```
-If you are using npm and wish to apply webpack, please continue to the next page: Quick Start.
+If you are using npm and wish to apply webpack, please continue to the next page: Quick Start.