Fix deprecated function call in get_expression_tree

Author: amontoison

src/NLPSupport/get_expr_tree.jl

@@ -37,7 +37,7 @@ function get_expression_tree(adnlp::ADNLPModel)
   n = adnlp.meta.nvar
   Symbolics.@variables x[1:n]
   fun = adnlp.f(x)
-  obj_Expr = Symbolics._toexpr(fun)
+  obj_Expr = Symbolics.toexpr(fun)
   expr_tree =
     ExpressionTreeForge.transform_to_expr_tree(obj_Expr)::ExpressionTreeForge.Type_expr_tree
   return expr_tree