fix deprecation

internal/builtins/readfile.go

@@ -1,9 +1,9 @@
 package builtins
 
 import (
-	"io/ioutil"
 	"monkey/internal/object"
 	"monkey/internal/typing"
+	"os"
 )
 
 // ReadFile ...
@@ -17,7 +17,7 @@ func ReadFile(args ...object.Object) object.Object {
 	}
 
 	filename := args[0].(*object.String).Value
-	data, err := ioutil.ReadFile(filename)
+	data, err := os.ReadFile(filename)
 	if err != nil {
 		return newError("IOError: error reading from file %s: %s", filename, err)
 	}