update readme to correct setLocale function

Adds support for yml and yaml files

```js
app.__(locale, text, value);
```

* chore: test on node 12

* test: use mocha@4

Update benchmark to version 2.0.0 🚀

http://greenkeeper.io/

PR-URL: https://github.com/koajs/locales/pull/17
Reviewed-By: fengmk2 <[email protected]>
Review...

fix: if header sent, don't set the cookie

bigpipe will fail

doc(options.dirs): fix api doc

refact(es6): use es6 syntax.

* fixed #10, But iojs-2 not support Object.assign, so use object-assign
shim instead for now.
...

refact(nested-data): transform nested data on load localization data.

feat: Support nested locale keys.

Example:

```js
{
model: {
user: {
name: 'Real Name',
createdAt: 'Joined At'
...

fix: merge-descriptors should be in dependencies

closes #8

Multiple locale paths support.

refact(apply): apply is not too slow than direct call. fixed #2

refact(endsWith): endsWith is fast than regexp

revert slice arguments to args

- revert 4ecffe8d22368f4a2cb65113600d9a514b10274e
- also add benchmark

feat: paramter support object

Patch

see https://github.com/petkaantonov/bluebird/wiki/Optimization-killers#3-managing-arguments