Bump plugin version to 2.0.20
Bump plugin version to 2.0.20

Shopify/airbrake,kakra/hoptoad_notifier,airbrake/airbrake,thoughtbot/hoptoad_notifier,square/hoptoad_notifier,nick-desteffen/airbrake,thoughtbot/airbrake,CarlosCD/airbrake,CarlosCD/airbrake,nick-desteffen/airbrake,stevecrozz/hydraulic_brake,benjaminoakes/airbrake,airbrake/airbrake