Format dashboard total downloads count
Format dashboard total downloads count

Use the format-num helper to properly comma-seperate the "Total Downloads" count
on the Dashboard page.

Fixes #855

rust-lang/crates.io,rust-lang/crates.io,steveklabnik/crates.io,rust-lang/crates.io,steveklabnik/crates.io,steveklabnik/crates.io,steveklabnik/crates.io,rust-lang/crates.io