runtime(termdebug): Fix wrong test for balloon feature

fixes: #15359
closes: #15487

Signed-off-by: Ubaldo Tiberi <ubaldo.tiberi@google.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/pack/dist/opt/termdebug/plugin/termdebug.vim b/runtime/pack/dist/opt/termdebug/plugin/termdebug.vim
index 04f82bd..377827e 100644
--- a/runtime/pack/dist/opt/termdebug/plugin/termdebug.vim
+++ b/runtime/pack/dist/opt/termdebug/plugin/termdebug.vim
@@ -1536,7 +1536,7 @@
 enddef
 
 def Balloon_show(expr: string)
-  if has("+balloon_eval") || has("+balloon_eval_term")
+  if has("balloon_eval") || has("balloon_eval_term")
     balloon_show(expr)
   endif
 enddef