Update modifier.rst

[kalpit3d]

Noramalize operation make list to range from 0 to 1, it was written as -1 to 1 which is incorrect.

Addressed problem description

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Solution description

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Preflight checklist

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• [ ] Code changes complete.
• [ ] Code documentation complete.
• [ ] Documentation for users complete (or not required, if user never sees these changes).
• [ ] Manual testing done.
• [ ] Unit-tests implemented.
• [ ] Ready for merge.