Como alinhar corretamente uma galeria de itens com flexbox?

.container {
  display: flex;
  justify-content: center;
  width: 100%;
}

.container-inner {
  display: flex;
  flex-wrap: wrap;
  justify-content: flex-start;
  width: calc(146px * 3)
}

.item {
  max-width: 136px;
  flex: 1 0 136px;
  margin: 0 5px 20px;
}

<div class="container">
  <div class="container-inner">
    <div class="item">
      <img src="http://placekitten.com/136">
    </div>
    <div class="item">
      <img src="http://placekitten.com/136">
    </div>
    <div class="item">
      <img src="http://placekitten.com/136">
    </div>
    <div class="item">
      <img src="http://placekitten.com/136">
    </div>
  </div>
</div>