lib: Update documentation example for proc_macro_mod inclusion?
lib: Update documentation example for proc_macro_mod inclusion?

I'm not even sure we need this, but since this feature gate hasn't been
stabilized I guess we still need this. (If I remove #![feature(proc_macro_hygiene)]
from the tests, the builds go red.)

Signed-off-by: Kristofer Rye <1ed31cfd0b53bc3d1689a6fee6dbfc9507dffd22@gmail.com>

CodeSandwich/Mocktopus