Let `transition` be an array

[antongolub]

transitions: {
        'init>loading': true,
        'loading>ok': (state, res) => res,
        'loading>err': (state, res) => res,
        'ok>loading': true,
        'err>loading': true
      }

↓

transitions: [
        'init>loading'
        ['loading>ok', (state, res) => res],
        ['loading>err', (state, res) => res],
        'ok>loading',
        'err>loading'
      ]