Typo: Missing & in match bindings examples

[scottmcm]

https://github.com/rust-lang-nursery/edition-guide/blame/master/src/2018/transitioning/ownership-and-lifetimes/default-match-bindings.md#L20

This has let s: &Option<&str> = Some("hello");
But should be let s: &Option<&str> = &Some("hello");

In both examples.