Upgrade helmet version to 5.x

[yairasco]

koa-helmet/package.json

Line 30 in 3608f84

"helmet": "^4.4.1"

There's a new version for helmet package 5.1.1

[JorindeReijnierse]

Helmet is already on 6.0.0 by now.. Would be great if koa-helmet can upgrade too because right now I can't use it anymore because Helmet 4 is using outdated security headers (for instance the expect-ct header which is now deprecated but helmet-4 still uses it: helmetjs/helmet#310)

[julienw]

It's done now, I guess you can close this issue!

[venables]

Thanks folks, closing this!