SimpleStatefulLayout设置offline 重试button的style

app:offlineRetryText无效
因为
`// setState custom offline retry text
		if(a.hasValue(R.styleable.SflStatefulLayout_offlineRetryText)) {
			setOfflineText(a.getString(R.styleable.SflStatefulLayout_offlineRetryText));
		}`

希望能够增加SimpleStatefulLayout中retry button的style的api