[TASK] Adjust to new sass-lint rule

assets/icons/_icon-mixin.scss

@@ -1,6 +1,6 @@
 @mixin icon($name, $code, $prefix: 'ion-') {
   .#{$prefix}#{$name} {
-    &:before {
+    &::before {
       content: '#{$code}';
     }
   }

scss/modules/_leaflet.scss

@@ -12,7 +12,7 @@
     white-space: nowrap;
     z-index: 6;
 
-    &:before {
+    &::before {
       display: none;
     }
   }

scss/modules/_table.scss

@@ -62,7 +62,7 @@ th {
   }
 
   &.sort-up, &.sort-down {
-    &:after {
+    &::after {
       opacity: .4;
       visibility: visible;
     }