Replace deprecated MultiTerm add() method from Glemm parser

Change-Id: If1126b89447bfa1d427189ff27e9a73158549e4f
diff --git a/lib/KorAP/XML/Annotation/Glemm/Morpho.pm b/lib/KorAP/XML/Annotation/Glemm/Morpho.pm
index 61f4d9b..582d89b 100644
--- a/lib/KorAP/XML/Annotation/Glemm/Morpho.pm
+++ b/lib/KorAP/XML/Annotation/Glemm/Morpho.pm
@@ -40,8 +40,8 @@
           };
         };
 
-        $mtt->add(
-          term => 'glemm/l:' .
+        $mtt->add_by_term(
+          'glemm/l:' .
             ($composition ? '+' : '_') .
             ($derivation ? '+' : '_') .
             $lemma