Capitalize "Rust"

Co-authored-by: Mark Rousskov <mark.simulacrum@gmail.com>

library/std/src/time.rs

@@ -133,7 +133,7 @@ pub use core::time::FromFloatSecsError;
 /// if available, which is the case for all [tier 1] platforms.
 /// In practice such guarantees are – under rare circumstances – broken by hardware, virtualization
 /// or operating system bugs. To work around these bugs and platforms not offering monotonic clocks
-/// [`duration_since`], [`elapsed`] and [`sub`] saturate to zero. In older rust versions this
+/// [`duration_since`], [`elapsed`] and [`sub`] saturate to zero. In older Rust versions this
 /// lead to a panic instead. [`checked_duration_since`] can be used to detect and handle situations
 /// where monotonicity is violated, or `Instant`s are subtracted in the wrong order.
 ///