Wrong number of elements when creating minibatchlist

[araffin]

Hello,

It seems that when creating the minibatchlist (main.py#L121), the wrong total number of element is used (because all last observation of each episode is removed):

minibatchlist = [np.array(sorted(indices[start_idx:start_idx + self.batchsize]))
                for start_idx in range(0, num_samples - self.batchsize + 1, self.batchsize)]

indices has not a length of num_samples, so instead of num_samples - self.batchsize + 1, it should be len(indices) - self.batchsize + 1:

minibatchlist = [np.array(sorted(indices[start_idx:start_idx + self.batch_size]))
                 for start_idx in range(0, len(indices) - self.batchsize + 1, self.batch_size)]

In fact, the current code always works when we have num_episodes < batchsize, but breaks when we have a lot of episodes ( num_episodes > 2 * batchsize).

this bug was spotted by @Elovir and @hill-a