An evaluation of non-melanoma skin cancer and melanoma skin cancer rates among patients treated for moderately to severely active rheumatoid arthritis with Xeljanz® (tofacitinib citrate): A retrospective non-interventional database study of observational data embedded within Optimising Patient outcome in Australian RheumatoLogy - Quality Use of Medicines Initiative (OPAL-QUMI) (Skin cancer rates in OpaL - SOL study)