chore(devdeps): update dependency koa to v2.10.0

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
koa	devDependencies	minor	2.8.2 -> 2.10.0

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Release Notes

koajs/koa

### [`v2.10.0`](https://togithub.com/koajs/koa/blob/master/History.md#​2100--2019-10-12) [Compare Source](https://togithub.com/koajs/koa/compare/2.9.0...2.10.0) ================== **features** - \[[`d7f7f77`](http://github.com/koajs/koa/commit/d7f7f77689e2eaef050686be2bdf3e72881a79ac)] - feat: support sameSite=none cookies (bump cookies dependency) ([#​1390](https://togithub.com/koajs/koa/issues/1390)) (Filip Skokan >) ### [`v2.9.0`](https://togithub.com/koajs/koa/blob/master/History.md#​290--2019-10-12) [Compare Source](https://togithub.com/koajs/koa/compare/2.8.2...2.9.0) ================== **features** - \[[`2d1c598`](http://github.com/koajs/koa/commit/2d1c5981869e0fe6f5bc71b5c5582accfd125cc6)] - feat: export HttpError from http-errors library (Micheal Hill >) **others** - \[[`cf70dbc`](http://github.com/koajs/koa/commit/cf70dbc6d2ba62bf1eb12b563dd5ecd27af6e2be)] - Chore: Use https in readme ([#​1389](https://togithub.com/koajs/koa/issues/1389)) (谭九鼎 >)

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