Heading parsing issue.

[n-hor]

Describe the bug
The heading is not parsed.

The delta code which generates the Problem

{
"ops": [
    {
      "attributes": {
        "background": "transparent",
        "color": "#000000"
      },
      "insert": "Header"
    },
    {
      "attributes": {
        "align": "center",
        "header": 1
      },
      "insert": "\n"
    }
  ]
}

The expected html output the delta should produce

<h1 style="text-align: center;"><span style="color:#000000;background-color:transparent">Header</span></h1>

Actual result:

<p style="text-align: center;"><span style="background-color:transparent"><span style="color:#000000">Header</span></span></p>