set btn outside of if block

Hi

First off, thanks for this lib. It saved me the effort :)

I was trying to use the lib to clip to an existing element on my page but could not get it to work. When I checked the source, I saw that the btn variable was only ever set in the if(!attrs.id) block and so the zeroclipboard client was not being created in the case where I was trying to clip to an element with an id.