Rollup merge of rust-lang#40621 - jswalden:dependant-spelling-fix, r=…

…sfackler

Fix a spelling error in HashMap documentation, and slightly reword surrounding text for precision

Noticed while reading docs just now.

It's possible that the prior wording *meant* to state that the seed's randomness depends on the exact instant that the system RNG was created, I guess.  But unless there's an API guarantee that this is the case, the wording seems over-precise.  Is there a formal API guarantee that would forbid, say, the system RNG from generating all output using the Intel RDRAND instruction?  I don't think the quality of output in that case would depend on when the RNG was created.  Yet it seems to me like it could well be a valid source of randomness when computing the initial seed.

For that reason, tying the randomness of the seed, to the quality of the RNG's output *at the precise instant the seed is computed*, seems less confining.  That instantaneous quality level could be determined by the quality at the instant the RNG was created -- but instantaneous quality need not be low for that precise reason.

src/libstd/collections/hash/map.rs

@@ -222,8 +222,8 @@ const DISPLACEMENT_THRESHOLD: usize = 128;
 /// resistance against HashDoS attacks. The algorithm is randomly seeded, and a
 /// reasonable best-effort is made to generate this seed from a high quality,
 /// secure source of randomness provided by the host without blocking the
-/// program. Because of this, the randomness of the seed is dependant on the
-/// quality of the system's random number generator at the time it is created.
+/// program. Because of this, the randomness of the seed depends on the output
+/// quality of the system's random number generator when the seed is created.
 /// In particular, seeds generated when the system's entropy pool is abnormally
 /// low such as during system boot may be of a lower quality.
 ///