Update chapter-09.md
Update chapter-09.md

Grabbing the second number with `.get(1)`
dskecse/rust_for_rubyists,steveklabnik/rust_for_rubyists,steveklabnik/rust_for_rubyists,gpbonillas/rust_for_rubyists,gpbonillas/rust_for_rubyists,dskecse/rust_for_rubyists,gpbonillas/rust_for_rubyists,dskecse/rust_for_rubyists,steveklabnik/rust_for_rubyists