docs(spinner): changed CSS selector for theming (#8047)
docs(spinner): changed CSS selector for theming (#8047)

Per: https://forum.ionicframework.com/t/ion-spinner-color/46324/6
alan-agius4/ionic,alan-agius4/ionic,manucorporat/ionic,dennybiasiolli/ionic,alan-agius4/ionic,joshesp/ionic,jhlee8804/ionic,manucorporat/ionic,joshesp/ionic,alan-agius4/ionic,manucorporat/ionic,jhlee8804/ionic,dennybiasiolli/ionic,driftyco/ionic,dennybiasiolli/ionic,driftyco/ionic,cambronjay/ionic,TillaTheHun0/ionic,TillaTheHun0/ionic,alan-agius4/ionic,joshesp/ionic,AbraaoAlves/ionic,cambronjay/ionic,jhlee8804/ionic,brianespinosa/ionic2-sass,joshesp/ionic,AbraaoAlves/ionic,dennybiasiolli/ionic,jhlee8804/ionic,jhlee8804/ionic,TillaTheHun0/ionic,cambronjay/ionic,cambronjay/ionic,AbraaoAlves/ionic,alan-agius4/ionic,driftyco/ionic,manucorporat/ionic,driftyco/ionic,manucorporat/ionic,driftyco/ionic,cambronjay/ionic,dennybiasiolli/ionic,TillaTheHun0/ionic,AbraaoAlves/ionic,AbraaoAlves/ionic