dependency fix: bitarray v1.5.1

[a1exlism]

Due to the update of bitarray(refer HERE)

2021-04-14 2.0.0:

• remove .length() method (deprecated since 1.5.1 - use len())

the codes in fromfile method update with len() instead of .length().

Code tested after the update.

[Meiple]

I had the same problem in my code and the error was:
AttributeError: 'bitarray.bitarray' object has no attribute 'length'
I change for len() and went from this filter.bitarray.length() to this len(filter.bitarray)