add Promise snippet to js-mode (since ES2015) (#228)
add Promise snippet to js-mode (since ES2015) (#228)

For details, see below link:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/promise
ageekymonk/yasnippet-snippets,ageekymonk/yasnippet-snippets,ageekymonk/yasnippet-snippets