Fix Apollo mutations update hooks to follow the immutability patters

In Apollo 2.6 there is a new option available helping us to enforce the immutability on update hooks. I.e. instead of

data.comments.push(newComment);

client.writeQuery({
  query: CommentQuery,
  data,
});

we should have

client.writeQuery({
  query: CommentQuery,
  data: {
    ...data,
    comments: [
      ...data.comments,
      newComment,
    ],
  },
});

The reasoning behind following an immutability pattern is explained in this article