Avoid using deprecated Buffer constructor

[ChALkeR]

safe-buffer is already used and provides Buffer.alloc polyfill, so just use Buffer.alloc directly to avoid hitting deprecated API.

Refs:
https://nodejs.org/api/deprecations.html#deprecations_dep0005_buffer_constructor

This was overlooked in 3d94b8c (#2484).

Tracking: nodejs/node#19079

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[dignifiedquire]

thank you lgtm