Changed Output API documentation _outputHelper to _reqnrollOutputHelper in constructor

[Sjors-Hoogenboom]

🤔 What's changed?

I changed the documentation output API constructor to contain _reqnrollOutputHelper instead of _outputHelper

⚡️ What's your motivation?

I noticed this small error while reading the documentation

🏷️ What kind of change is this?

• 📖 Documentation (improvements without changing code)

♻️ Anything particular you want feedback on?

Not sure if refacotring the field to _outputHelper would've been more appriciated than changing the constructor

📋 Checklist:

• I've changed the behaviour of the code
  • I have added/updated tests to cover my changes.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• Users should know about my change
  • I have added an entry to the "[vNext]" section of the CHANGELOG, linking to this pull request & included my GitHub handle to the release contributors list.

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