Update bloom_filter.py

[agarwl]

Fix incorrect use of XOR operator to use correct POWER operator. In Python "2 ^ N" means "2 XOR N" whereas "2 ** N" means "2 to the power N". The fact that this change still passes all tests either indicates that there are serious test flaws.

[remram44]

There's actually another one further down in File_seek_backend