Fix issue with premise of buyer in haggling environment

[RisingOrange]

There is an mistake in the premise of the buyer in the haggling environment.

Currently it says:
"Buyer is trying to buy some fruit from Seller. They are negotiating a price. Seller can sell the fruit for buyer_base_reward coins back in her home town."

It would make more sense if it would say this:
"Buyer is trying to buy some fruit from Seller. They are negotiating a price. Buyer can sell the fruit for buyer_base_reward coins back in her home town."

The buyer intends to sell the fruit (which she bought from the seller) in her home town.
This fits with the score of the buyer being the buyer_base_reward - the price they paid to buy the fruit:

concordia/concordia/contrib/components/game_master/bargain_payoffs.py

Lines 186 to 189 in c35440e

	if accepted:
	rewards[self._buyer.name] = (
	self._buyer_base_reward - self._action_to_reward[proposal]
	)

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[vezhnick]

Thanks!