docs: TOC shows text not anchor link

For example, if the title has upper case characters,
the anchor is in lower case. Use innerText instead.

Test: see kleaf docs
Change-Id: I0f9cefe4b3aa5627ab422fedf7cd8263277cb1b2
diff --git a/docs/index.html b/docs/index.html
index 9c5c171..66cd737 100644
--- a/docs/index.html
+++ b/docs/index.html
@@ -51,7 +51,7 @@
                 var clone = sampleTocItem.cloneNode(true)
                 var link = clone.getElementsByTagName("a")[0];
                 link.href = "#" + h2Elements[i].id
-                link.innerText = h2Elements[i].id
+                link.innerText = h2Elements[i].innerText
                 toc.appendChild(clone)
             }
             toc.appendChild(document.getElementById("div-sample-toc-break").cloneNode(true))