Updates and improvements

[lagden]

• change test framework mocha -> ava and istanbul -> nyc
• prefer async/await
• add xo lint (eslint)
• travis run nodejs 8 LTS

[coveralls]

Coverage remained the same at 100.0% when pulling 3524318 on lagden:master into 4b19eb1 on koajs:master.

[haoxins]

• eslint: we have https://github.com/koajs/eslint-config-koa
• disable package-lock

change test framework mocha -> ava and istanbul -> nyc

why ?

[lagden]

I didn't know about eslint-config-koa...
added!

why?

Mocha requires you to use implicit globals like describe and it with the default interface (which most people use). It's not very opinionated and executes tests serially without process isolation, making it slow.

[jonathanong]

generally styling fixes are not accepted. i would take the .travis.yml updates though

[jonathanong]

and @coderhaoxin 's suggestions

[lagden]

@jonathanong

the style is according with the eslint-config-koa

https://github.com/lagden/conditional-get/blob/3524318c7c854efd479b75bd2fac182c7388029e/package.json#L41

and mocha -> ava was "upgrade", but the test content is the same...

Any further suggestions?

[haoxins]

#13