Fix little CSS issue with required input attribute 

You use .css({'position':'absolute','left':'-9999px'}) to original button hiding. But, when the "required" attribute is set for this input, and user forgot to pick the file, browser show alarm on the leftmost window edge due to -9999.

Better way to avoid this - using .css({'position':'absolute','clip':'rect(0,0,0,0)'})
https://github.com/markusslima/bootstrap-filestyle/issues/45