fix: lists will remove duplicate elements when merging yaml.

This will solve the duplicate warning that docker-compose issues
notably on ``links``.

bin/compose

@@ -78,7 +78,10 @@ def merge(*args):
     elif all(isinstance(arg, list) for arg in args):
         res = []
         for arg in args:
-            res.extend(arg)
+            for elt in arg:
+                if elt in res:
+                    res.remove(elt)
+                res.append(elt)
         return res
     elif all(isinstance(arg, dict) for arg in args):
         keys = set()