Merge pull request #11 from github/use-html-element-tag-name-map

Add HTMLElementTagNameMap interface to TypeScript declaration file.

index.d.ts

@@ -6,4 +6,7 @@ declare global {
   interface Window {
     TextExpanderElement: typeof TextExpanderElement
   }
-}
+  interface HTMLElementTagNameMap {
+    'text-expander': TextExpanderElement
+  }
+}