fix(Popover): correct ShadyCSS styles

Author: Cathy Siller

src/helix-ui/elements/HXPopoverElement.html

@@ -1,5 +1,5 @@
 <div class="position-arrow">
-  <div id="container">
+  <div id="hxPopover">
     <slot></slot>
   </div>
 </div>

src/helix-ui/elements/HXPopoverElement.less

@@ -1,6 +1,6 @@
 @import "./HXElement";
 @import "./_positioning";
 
-#container {
+#hxPopover {
   overflow: hidden;
 }