Update level.sass to fix issue with icons (#1193)

* Update level.sass

Removing `margin-right: 0.75rem` from the `level is-mobile` in #1153 changed the spacing of icons used in the `level-items`. This pr restores the margin-right for the icon class only to restore the behavior as before while keeping changes made in #1153.

* Update level.sass

the margin for icons should be only for level is-mobile.

* Update level.sass

* add margin-right to level-item

* add margin to .level.is-mobile .level-item

made suggested changes

sass/components/level.sass

@@ -20,6 +20,7 @@
         margin-bottom: 0
       &:not(.is-narrow)
         flex-grow: 1
+      margin-right: 0.75rem
   // Responsiveness
   +tablet
     display: flex
@@ -41,7 +42,7 @@
   +mobile
     &:not(:last-child)
       margin-bottom: 0.75rem
-
+    
 .level-left,
 .level-right
   flex-basis: auto