Fixes small typo in array docs r? @steveklabnik
Fixes small typo in array docs r? @steveklabnik

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