Allow adding string to number

Upsilon/Evaluator/Evaluator.cs

@@ -290,6 +290,10 @@ namespace Upsilon.Evaluator
                         {
                             return ((ScriptNumber)left) + ((ScriptNumber)right);
                         }
+                        if (right.Type == Type.String)
+                        {
+                            return new ScriptString(left + right.ToString());
+                        }
                     }
                     else if (left.Type == Type.String)
                     {