fix(mdToast): Puts index above dialog

Closes #903

Author: Marcy Sutton

src/core/style/variables.scss

@@ -58,8 +58,8 @@ $whiteframe-zindex-z5: 5;
 //--------------------------------------------
 
 $z-index-tooltip: 100;
-$z-index-dialog: 90;
-$z-index-toast: 80;
+$z-index-dialog: 80;
+$z-index-toast: 90;
 $z-index-bottom-sheet: 70;
 $z-index-sidenav: 60;
 $z-index-backdrop: 50;