Use QUnit `raises` instead of `throws`

`throws` is a future reserved word (http://www.ecma-international.org/publications/files/ECMA-ST-ARCH/ECMA-262,%203rd%20edition,%20December%201999.pdf), and using it causes problems with Closure Compiler and (reportedly) NarwhalJS (https://github.com/jquery/qunit/pull/323).

QUnit has `raises` as an alias.