preferXHR of FontLoader should be removed

[FumioNonaka]

PreloadJS/src/preloadjs/loaders/FontLoader.js

Line 40 in 7a3a39c

// constructor:

The second argument of FontLoader, preferXHR , is not documented. And FontLoader does not support tag-based loading. Therefore, it should be removed and pass true to the constructor of the superclass.

function FontLoader(loadItem) {
	this.AbstractLoader_constructor(loadItem, true, loadItem.type);