finagle: Add Fitbit to ADOPTERS.md
finagle: Add Fitbit to ADOPTERS.md

Signed-off-by: Ruben Oanta <roanta@twitter.com>

RB_ID=913526

twitter/finagle,koshelev/finagle,luciferous/finagle,twitter/finagle,luciferous/finagle,koshelev/finagle,twitter/finagle,mkhq/finagle,mkhq/finagle,twitter/finagle,koshelev/finagle,koshelev/finagle,koshelev/finagle,luciferous/finagle,luciferous/finagle,twitter/finagle,luciferous/finagle,mkhq/finagle,luciferous/finagle,mkhq/finagle,mkhq/finagle,koshelev/finagle,mkhq/finagle