docs(api): Added missing output flag in example. (webpack#2087)

Author: rencire

src/content/api/cli.md

@@ -6,6 +6,7 @@ contributors:
   - simon04
   - tbroadley
   - chenxsan
+  - rencire
   - madhavarshney
 related:
   - title: Analyzing Build Statistics
@@ -68,7 +69,7 @@ If your project structure is as follows -
 ```
 
 ```bash
-webpack ./src/index.js dist/bundle.js
+webpack src/index.js -o dist/bundle.js
 ```
 
 This will bundle your source code with entry as `index.js` and the output bundle file will have a path of `dist` and the filename will be `bundle.js`