flex-wrap doesn't work in iphone5 (ios 8)

Question

I want to use flexbox wrap to set one simple grid system. The css is:

.gridlayout__list {
   display: flex;
   flex-wrap: wrap;
  .gridlayout__item {
     flex: 1 0 49%; //这里留1%给边距
     min-width: 150px;
   }
}

PS: I have use the post-css to auto generate prefix

In iphone 6 it works well:

But in iphone 5, it doesn't work: