fix(button): normalize generated button class names
fix(button): normalize generated button class names

Addresses https://github.com/driftyco/ionic/issues/5938.

manucorporat/ionic,alan-agius4/ionic,alan-agius4/ionic,janglednerves/ionic,cambronjay/ionic,jhlee8804/ionic,alan-agius4/ionic,alan-agius4/ionic,manucorporat/ionic,AbraaoAlves/ionic,cambronjay/ionic,joshesp/ionic,joshesp/ionic,jarrodkoch/ionic,janglednerves/ionic,driftyco/ionic,alan-agius4/ionic,dennybiasiolli/ionic,TillaTheHun0/ionic,AbraaoAlves/ionic,driftyco/ionic,TillaTheHun0/ionic,cambronjay/ionic,janglednerves/ionic,joshesp/ionic,janglednerves/ionic,alan-agius4/ionic,manucorporat/ionic,driftyco/ionic,jhlee8804/ionic,joshesp/ionic,jarrodkoch/ionic,dennybiasiolli/ionic,TillaTheHun0/ionic,dennybiasiolli/ionic,driftyco/ionic,AbraaoAlves/ionic,brianespinosa/ionic2-sass,jarrodkoch/ionic,AbraaoAlves/ionic,jhlee8804/ionic,cambronjay/ionic,manucorporat/ionic,AbraaoAlves/ionic,jhlee8804/ionic,manucorporat/ionic,dennybiasiolli/ionic,TillaTheHun0/ionic,jhlee8804/ionic,driftyco/ionic,cambronjay/ionic,janglednerves/ionic,jarrodkoch/ionic,dennybiasiolli/ionic,jarrodkoch/ionic