Fix comparator, std::basic_string::compare returns an int, not bool.
Fix comparator, std::basic_string::compare returns an int, not bool.

PiperOrigin-RevId: 422597321
Change-Id: Icc691a499767e72f5fb2086bedeef3ed2d6a1994

deepmind/open_spiel,deepmind/open_spiel,deepmind/open_spiel,deepmind/open_spiel,deepmind/open_spiel,deepmind/open_spiel