Allow compressed dependencies

[elliothershberg]

Hi! Thanks for the fantastic package. I've been building a htmlwidget, and am now trying to optimize bundle size. I am using reactR, and creating my widget dependency with webpack. I'm trying to use a webpack compression plugin.

My dependency is much smaller, but now is a .js.gz file, which doesn't get discovered by htmlwidgets. Would it be possible to update this function to look for a .js file or a .js.gz file?

htmlwidgets/R/utils.R

Lines 39 to 46 in 31dd945

	#' Get js and css dependencies for a htmlwidget
	#'
	#' @param name name of the widget.
	#' @param package name of the package, defaults to the widget name.
	#' @export
	getDependency <- function(name, package = name){
	config = sprintf("htmlwidgets/%s.yaml", name)
	jsfile = sprintf("htmlwidgets/%s.js", name)