Updated sizes for gl-loading-icon

Changed from numeric sizes to string sizes.
Fixes issue:
  Icon sizes 1 - 5 are deprecated,
  please use 'sm', 'md' and 'lg' instead.

app/assets/javascripts/environments/components/container.vue

@@ -41,7 +41,7 @@ export default {
   <div class="environments-container">
     <gl-loading-icon
       v-if="isLoading"
-      :size="3"
+      size="md"
       class="prepend-top-default"
       label="Loading environments"
     />

app/assets/javascripts/environments/components/environments_table.vue

@@ -170,7 +170,7 @@ export default {
 
       <template v-if="shouldRenderFolderContent(model)">
         <div v-if="model.isLoadingFolderContent" :key="`loading-item-${i}`">
-          <gl-loading-icon :size="2" class="prepend-top-16" />
+          <gl-loading-icon size="md" class="prepend-top-16" />
         </div>
 
         <template v-else>