fix: correct notebook install hint

[Ankit-Kotnala]

Summary

• Correct the play(..., notebook=True) missing dependency message so it references notebook=True instead of notebook=False.

Verification

• python -m py_compile src/elevenlabs/play.py

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Note

Low Risk
Low risk: changes only a user-facing error string and does not affect audio playback logic or dependencies.

Overview
Fixes a misleading error message in play() so the IPython install hint correctly says it’s required when notebook=True (instead of notebook=False).

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[Ankit-Kotnala]

Hi @kraenhansen, when you have a moment, could you please review this small PR? It’s a one-line fix to correct the notebook-mode install hint in play(). Thanks!

[kraenhansen]

Thanks!