Update example for get_array_statistics

[j08lue]

I noticed that the example in https://cogeotiff.github.io/rio-tiler/advanced/statistics/#area-weighted-statistics was not yet updated after your changes in

• fix statistics for coverage #684

This copies the latest code from the respective test into the docs page

rio-tiler/tests/test_utils.py

Lines 573 to 592 in 062420a

	# Data Array
	# 1, 2
	# 3, 4
	data = np.ma.array((1, 2, 3, 4)).reshape((1, 2, 2))
	# Coverage Array
	# 0.5, 0
	# 1, 0.25
	coverage = np.array((0.5, 0, 1, 0.25)).reshape((2, 2))
	stats = utils.get_array_statistics(data, coverage=coverage)
	assert len(stats) == 1
	assert stats[0]["min"] == 1
	assert stats[0]["max"] == 4
	assert (
	round(stats[0]["mean"], 4) == 2.5714
	) # sum of weighted array / sum of weights | 4.5 / 1.75 = 2.57
	assert stats[0]["count"] == 1.75
	assert stats[0]["median"] == 3 # 2 in exactextract
	assert round(stats[0]["std"], 2) == 1.05