Change `id` to `identity` in documentation

[janeymunoz]

Relevant since this change to Prelude: purescript/purescript-prelude@2f11d6f

Instances of id in URI documentation: https://github.com/purescript-contrib/purescript-uri/search?q=id&unscoped_q=id

[garyb]

Resolved by #52