Fix: DOM elements don't match `e instanceof HTMLElement`

I don't know what changed regarding that but it is not
the first time I see gr-diff DOM elements not returning true
for this statement. In practice here it prevents annotation to
happen in deeper levels - example: token highlighting conflicts
with intraline information.

Change-Id: I969e280d3d98418df127bc5be5dadf29c03ce48c
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-highlight/gr-annotation.ts b/polygerrit-ui/app/elements/diff/gr-diff-highlight/gr-annotation.ts
index 5e81871..79e7dbc 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-highlight/gr-annotation.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-highlight/gr-annotation.ts
@@ -134,7 +134,7 @@
 
       if (node instanceof Text) {
         this._annotateText(node, offset, subLength, cssClass);
-      } else if (node instanceof HTMLElement) {
+      } else if (node instanceof Element) {
         this.annotateElement(node, offset, subLength, cssClass);
       }