make REL_BLACKLIST editable

Author: JuliusFiedler

src/pyirk/visualization.py

@@ -351,10 +351,10 @@ def add_node(self, node: AbstractGraphObject, **kwargs):
 class VisualizationManager():
 
     def __init__(self):
-        self.REL_BLACKLIST = (
+        self.REL_BLACKLIST = [
             "irk:/builtins#R1",
             "irk:/builtins#R2",
-        )
+        ]