Properly handle negater, if not default

Signed-off-by: martin f. krafft <madduck@madduck.net>
diff --git a/reclass/datatypes/applications.py b/reclass/datatypes/applications.py
index 92411b6..3074e6b 100644
--- a/reclass/datatypes/applications.py
+++ b/reclass/datatypes/applications.py
@@ -16,8 +16,8 @@
     def _combine(self, first, second):
         for i in second:
             remove = False
-            if i.startswith('~'):
-                i = i[1:]
+            if i.startswith(self._negater):
+                i = i[len(self._negater):]
                 remove = True
             if i not in first:
                 if not remove: