Customizer: For consistency, use singular in JS components list of Less files

Author: cvrebert

docs/customize.html

@@ -237,25 +237,25 @@ <h3>JavaScript components</h3>
         <div class="checkbox">
           <label>
             <input type="checkbox" checked value="dropdowns.less">
-            Dropdowns
+            Dropdown
           </label>
         </div>
         <div class="checkbox">
           <label>
             <input type="checkbox" checked value="tooltip.less">
-            Tooltips
+            Tooltip
           </label>
         </div>
         <div class="checkbox">
           <label>
             <input type="checkbox" checked value="popovers.less">
-            Popovers
+            Popover
           </label>
         </div>
         <div class="checkbox">
           <label>
             <input type="checkbox" checked value="modals.less">
-            Modals
+            Modal
           </label>
         </div>
         <div class="checkbox">