time async properly with `Promise`
time async properly with `Promise`

@note In Node 0.12.0 `.then()` still processed wrongly, thus results will be printed before actual task will be finished, but basically it works anyway

ArmorDarks/grunt-nunjucks-2-html,ArmorDarks/grunt-nunjucks-2-html,vitkarpov/grunt-nunjucks-2-html,vitkarpov/grunt-nunjucks-2-html