Default sweep broken for most envs

[FrostyFridge]

Currently puffer sweep bombs out for most envs.

ex.

$ puffer sweep breakout
[...]
AssertionError: Param match_enemy_model_path is not a dict

Likely culprit appears to be recent PR #564 which seems to have edited the base sweep settings section with some env-specific settings.

PufferLib/config/default.ini

Lines 103 to 109 in e90b58e

	# When set, each sweep trial is scored by winrate in a match against a fixed
	# enemy checkpoint rather than by the training-time env/score. Score key emitted
	# as env/match_score; set match_enemy_model_path to '' to disable.
	match_enemy_model_path = ''
	match_num_games = 1024
	match_enemy_hidden_size = 0
	match_enemy_num_layers = 0