MeanSquaredError and MeanAbsoluteError Metrics use old argument names

[cgarciae]

Since recently we've been using the following convention for the arguments for Metric's update function:

• y_pred => preds
• y_true => target

However, MeanSquareError and MeanAbsoluteError use the old convention:

treex/treex/metrics/mean_square_error.py

Lines 64 to 69 in 3aa5415

	def update(
	self,
	y_true: jnp.ndarray,
	y_pred: jnp.ndarray,
	sample_weight: jnp.ndarray = None,
	) -> tp.Any:

treex/treex/metrics/mean_absolute_error.py

Lines 64 to 69 in 3aa5415

	def update(
	self,
	y_true: jnp.ndarray,
	y_pred: jnp.ndarray,
	sample_weight: jnp.ndarray = None,
	) -> tp.Any:

This is not a hard issue for Treex itself but Elegy does rely on this convention and it makes these metrics incompatible (poets-ai/elegy#216).

cc: @anvelezec @jmarrietar