bug when logging events with an event value of 0

[sjungwirth]

When logging multiple events, if an event (not the first) has an event value of zero (0), it is discarded due to these lines:

universal-analytics/lib/index.js

Line 232 in 0e94cf8

params.ev = value || params.ev || this._context.ev;

universal-analytics/lib/index.js

Lines 536 to 543 in 0e94cf8

	_tidyParameters: function (params) {
	for (var param in params) {
	if (params[param] === null || params[param] === undefined) {
	delete params[param];
	}
	}
	return params;
	},

This combined with the batch request will result in the event inheriting the value from the previous event when it is processed by GA.