[gnome-calculator/wip/ricotz/vala] Use GLib.List.deep_copy() to fix type-argument mismatch

[Rico Tzschichholz <ricotz src gnome org>]

commit d89466a7e90d95b8a34fc0a3db6007599b243788
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Sun Nov 4 19:41:23 2018 +0100

    Use GLib.List.deep_copy() to fix type-argument mismatch

 lib/equation-parser.vala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/lib/equation-parser.vala b/lib/equation-parser.vala
index 56acf166..889b5d7f 100644
--- a/lib/equation-parser.vala
+++ b/lib/equation-parser.vala
@@ -76,7 +76,7 @@ public class ParseNode : Object
     public ParseNode.WithList (Parser parser, List<LexerToken> token_list, uint precedence, Associativity 
associativity, string? value = null)
     {
         this.parser = parser;
-        this.token_list = token_list.copy();
+        this.token_list = token_list.copy_deep((CopyFunc) Object.ref);
         this.precedence = precedence;
         this.associativity = associativity;
         this.value = value;