title: insert_all does not match type :utc_datetime
body: <p>So I have an <strong>array of objects</strong> that i want to save using <code>insert_all</code>. Im getting an error that one of my fields does not match.</p>
  
  <p><strong>edtr.json</strong></p>
  
  <pre><code>{
  "edtrs":
  [
      {
          "dtr_date": "2018-12-29T16:00:00.000Z",
          "user_id": "8189f04b-e3d7-4d17-8df2-fedbeb0399b1"
      },
      {
          "dtr_date": "2018-12-30T16:00:00.000Z",
          "user_id": "8189f04b-e3d7-4d17-8df2-fedbeb0399b1"
      }
  ]}
  </code></pre>
  
  <p><strong>post_controller</strong></p>
  
  <pre><code> def create_edtr(edtrs) do
  maps =
    Enum.map(edtrs["edtrs"], fn(item) -&gt;
      %{dtr_date: item["dtr_date"], user_id: item["user_id"]}
    end)
  
  IO.inspect maps, label: "MAPS"
  Repo.insert_all(Edtr,maps) end
  </code></pre>
  
  <p><strong>ERROR</strong></p>
  
  <blockquote>
    <p><code>HrisApp.Attendance.Edtr.dtr_date</code> in <code>insert_all</code> does not match type <code>:utc_datetime</code></p>
  </blockquote>