Add "anno-mundi" and "ethiopic" for ethiopic

Use "anno-mundi" and "ethiopic" for ethiopic calendar

Author: FrankYFTang

spec.emu

@@ -66,7 +66,7 @@ contributors: Google, Ecma International
       </tr>
       <tr>
         <td>*"ethiopic"*</td>
-        <td> ???? </td>
+        <td>*"anno-mundi"*, *"ethiopic"*</td>
         <td>*"M13"*</td>
       </tr>
       <tr>