Update pure_new option comment

[watame]

Hello! 👋

I changed the comment because the comment for the pure_new option was the same as pure_func.
I inferred the behavior from RSpec and Terser documentation, and wrote the comments, but since I'm not a native speaker, the English might be odd.

Could you review it to see if it's correct?

Reference URL

• https://terser.org/docs/options/

Thanks 🙏

[ahorek]

it's exactly what the option does. Thanks for improving the documentation!