fix(checkbox): center align stacked labels

Author: brandyscarney

core/src/components/checkbox/checkbox.common.scss

@@ -179,6 +179,8 @@
  */
 :host(.checkbox-label-placement-stacked) .checkbox-wrapper {
   flex-direction: column;
+
+  text-align: center;
 }
 
 :host(.checkbox-label-placement-stacked.checkbox-alignment-start) .label-text-wrapper {

core/src/components/checkbox/checkbox.native.scss

@@ -128,10 +128,6 @@ input {
 // Label Placement - Stacked
 // ----------------------------------------------------------------
 
-:host(.checkbox-label-placement-stacked) .checkbox-wrapper {
-  text-align: center;
-}
-
 :host(.checkbox-label-placement-stacked) .label-text-wrapper {
   @include transform(scale(#{$form-control-label-stacked-scale}));