Example in README duplicates img tags

[johnbeech]

Test file:

const json2md = require("json2md")

console.log(json2md([
    { h1: "JSON To Markdown" }
  , { blockquote: "A JSON to Markdown converter." }
  , { img: [
        { title: "Some image", source: "https://example.com/some-image.png" }
      , { title: "Another image", source: "https://example.com/some-image1.png" }
      , { title: "Yet another image", source: "https://example.com/some-image2.png" }
      ]
    }
  , { h2: "Features" }
  , { ul: [
        "Easy to use"
      , "You can programmatically generate Markdown content"
      , "..."
      ]
    }
  , { h2: "How to contribute" }
  , { ol: [
        "Fork the project"
      , "Create your branch"
      , "Raise a pull request"
      ]
    }
  , { h2: "Code blocks" }
  , { p: "Below you can see a code block example." }
  , { "code": {
        language: "js"
      , content: [
          "function sum (a, b) {"
        , "   return a + b"
        , "}"
        , "sum(1, 2)"
        ]
      }
    }
]))

Actual output:

  # JSON To Markdown

  > A JSON to Markdown converter.

  ![](https://example.com/some-image.png "Some image")
  ![](https://example.com/some-image.png "Some image")

  ![](https://example.com/some-image1.png "Another image")
  ![](https://example.com/some-image1.png "Another image")

  ![](https://example.com/some-image2.png "Yet another image")
  ![](https://example.com/some-image2.png "Yet another image")


  ## Features


  - Easy to use
  - You can programmatically generate Markdown content
  - ...

  ## How to contribute


  1. Fork the project
  2. Create your branch
  3. Raise a pull request

  ## Code blocks


  Below you can see a code block example.

  ```js
  function sum (a, b) {
     return a + b
  }
  sum(1, 2)
  ```

Note the duplicated images; three in the input, three pairs, six total images in the output.

[johnbeech]

Created a PR with a test case to demonstrate the issue:

• #98