Update jquery.multiselect.js

Allow width options for the button and menu elements.

Options:
buttonWidth: 'inherit', //set the width of the button. "inherit" will use the width from the select, "auto" will auto size, any other value will be directly applied
menuWidth: 'button',//set the width of the menu. "inherit" will use the width from the select, "auto" will auto size, "button" will take it's size from the button, any other value will be directly applied