Incorrect docs for undersample and oversample

[Moelf]

The docs claims:

MLUtils.jl/src/resample.jl

Lines 133 to 141 in b29bf41

	X_bal, Y_bal = undersample(X, Y)
	# this results in a smaller dataset
	@assert size(X_bal) == (3,4)
	@assert length(Y_bal) == 4
	# now both "a", and "b" have 2 observations each
	@assert sum(Y_bal .== "a") == 2
	@assert sum(Y_bal .== "b") == 2

The docs needs to be changed to ((X,Y))

same goes for oversample.

[Moelf]