Enable object shorthand syntax rule (object-shorthand)

[robertrossmann]

Enable coding style rule which prefers object shorthands instead of the classic ES5 object syntax.

Before

const param1 = 'abc'
const param2 = 'def'

const obj = { param1: param1, param2: param2, param3: 'ghi' }

After

const param1 = 'abc'
const param2 = 'def'

const obj = { param1, param2, param3: 'ghi' }