Fix import: sympy.numbers -> sympy.core.numbers

Apparently sympy no longer exports sympy.numbers directly.

pystencils/sympyextensions.py

@@ -260,8 +260,8 @@ def subs_additive(expr: sp.Expr, replacement: sp.Expr, subexpression: sp.Expr,
         if not param_list:
             return current_expr
         else:
-            if current_expr.func == sp.Mul and sp.numbers.Zero() in param_list:
-                return sp.numbers.Zero()
+            if current_expr.func == sp.Mul and sp.core.numbers.Zero() in param_list:
+                return sp.core.numbers.Zero()
             else:
                 return current_expr.func(*param_list, evaluate=False)