Fix documentation of Instant::now on mac

[stepancheg]

It is CLOCK_UPTIME_RAW on Apple.

rust/library/std/src/sys/pal/unix/time.rs

Lines 260 to 264 in b6f0945

	impl Instant {
	#[cfg(target_vendor = "apple")]
	pub(crate) const CLOCK_ID: libc::clockid_t = libc::CLOCK_UPTIME_RAW;
	#[cfg(not(target_vendor = "apple"))]
	pub(crate) const CLOCK_ID: libc::clockid_t = libc::CLOCK_MONOTONIC;

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