Bump koa from 2.7.0 to 2.11.0

Bumps [koa](https://github.com/koajs/koa) from 2.7.0 to 2.11.0.
- [Release notes](https://github.com/koajs/koa/releases)
- [Changelog](https://github.com/koajs/koa/blob/master/History.md)
- [Commits](https://github.com/koajs/koa/compare/2.7.0...2.11.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package.json

@@ -54,7 +54,7 @@
     "jimp": "^0.9.3",
     "jquery": "^3.3.1",
     "kcors": "^2.2.2",
-    "koa": "^2.7.0",
+    "koa": "^2.11.0",
     "koa-bodyparser": "^4.2.1",
     "koa-compress": "~3.0.0",
     "koa-csrf": "^3.0.7",