Replace REPLACEME's left out of 2.4.0

https://github.com/harfbuzz/harfbuzz/issues/1641
diff --git a/src/hb-common.h b/src/hb-common.h
index fbabd71..371b2bf 100644
--- a/src/hb-common.h
+++ b/src/hb-common.h
@@ -358,7 +358,7 @@
   /*11.0*/HB_SCRIPT_SOGDIAN			= HB_TAG ('S','o','g','d'),
 
   /*
-   * Since REPLACEME
+   * Since 2.4.0
    */
   /*12.0*/HB_SCRIPT_ELYMAIC			= HB_TAG ('E','l','y','m'),
   /*12.0*/HB_SCRIPT_NANDINAGARI			= HB_TAG ('N','a','n','d'),