Update lib/psych/scalar_scanner.rb

Co-authored-by: Olle Jonsson <olle.jonsson@gmail.com>

Author: OpakAlex

lib/psych/scalar_scanner.rb

@@ -16,7 +16,7 @@ class ScalarScanner
     # Taken from http://yaml.org/type/int.html
     INTEGER = /^(?:[-+]?0b[0-1_,]+                        (?# base 2)
                   |[-+]?0[0-7_,]+                         (?# base 8)
-                  |[-+]?(?:0|[1-9]([0-9]|,[0-9]|_[0-9])*) (?# base 10)
+                  |[-+]?(?:0|[1-9](?:[0-9]|,[0-9]|_[0-9])*) (?# base 10)
                   |[-+]?0x[0-9a-fA-F_,]+                  (?# base 16))$/x
 
     attr_reader :class_loader