Small bug in utils.py

[dsacc]

In distanz():

# Size verification
if rx != ry:
    raise("The sizes of x and y do not fit")

when the condition is met the following error message is returned:

TypeError: exceptions must derive from BaseException

Something like the following should fix it:

# Size verification
if rx != ry:
    raise ValueError("The sizes of x and y do not fit")