fix vcf FILTER column name

[gavin-peng]

utils.py line 191: vcf['FILTER_PASS'] == True)
this is filtering for a column called "FILTER_PASS". from what I can see in our vcf file, the column is just called FILTER, and the values are "PASS".
so the original filter condition will filter out all the variants, I guess that's the reason all the DeepTumour results give same prediction of cancer type regardless of inputs.
The fix added the condition for column name "FILTER".

[GFJHogue]

If this changes the behaviour for some VCF files, then there is likely a bug with scikit-allel. It's supposed to automatically create the FILTER_PASS column and populate it with True for all PASSing rows.

If this is indeed working around broken behaviour, then this change looks reasonable @gavin-peng

[gavin-peng]

If this changes the behaviour for some VCF files, then there is likely a bug with scikit-allel. It's supposed to automatically create the FILTER_PASS column and populate it with True for all PASSing rows.

If this is indeed working around broken behaviour, then this change looks reasonable @gavin-peng

thanks Greg!