Change mention of `fnv` in HashMap to mention `aHash` as an alternitive hasher.
Change mention of `fnv` in HashMap to mention `aHash` as an alternitive hasher.

Signed-off-by: Tom Kaitchuck <ca56a5f347880579ad16e22284df28d13a310849@emc.com>

graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust