fix: render bands properly not nested bands data

[jung-han]

Please check if the PR fulfills these requirements

• It's submitted to right branch according to our branching model
• It's right issue type on title
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes/features)
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• It does not introduce a breaking change or has description for the breaking change

Description

const options = {
  plot: {
    bands: [{
      range: [3, 8], // not working
      range: [[3, 8]], // working
    }]
  }
}

• render bands properly not nested bands data

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Thank you for your contribution to TOAST UI product. 🎉 😘 ✨

[lja1018]

리뷰완료합니다!

[js87zz]

리뷰 완료입니다~!

[jungeun-cho]

확인했습니다~!