Fix E and W flake8 errors

bob/bio/vein/algorithm/Correlate.py

bob/bio/vein/algorithm/MiuraMatch.py

bob/bio/vein/extractor/MaximumCurvature.py

bob/bio/vein/extractor/PrincipalCurvature.py

bob/bio/vein/extractor/RepeatedLineTracking.py

bob/bio/vein/extractor/WideLineDetector.py

bob/bio/vein/preprocessor/crop.py

bob/bio/vein/preprocessor/filters.py

bob/bio/vein/preprocessor/mask.py

bob/bio/vein/preprocessor/normalize.py

bob/bio/vein/preprocessor/utils.py

bob/bio/vein/script/view_sample.py

bob/bio/vein/tests/test_databases.py