fix keyword silliness

Author: James Halliday

lib/test.js

@@ -109,7 +109,7 @@ Test.prototype.skip = function (msg, extra) {
 };
 
 Test.prototype.ok
-= Test.prototype.true
+= Test.prototype['true']
 = Test.prototype.assert
 = function (value, msg, extra) {
     this._assert(value, {