Put newline after begin

Rendering `.js.erb` into `.html` will cause syntax errors of JavaScript.

![Example](https://cloud.githubusercontent.com/assets/139089/3810774/24b73296-1c95-11e4-8747-58d2ec893e10.png)

The HTML comment token tells web browser to skip the first line of the following JS program here.

Inserting newline after `<!-- BEGIN ... -->` solves this issue.