Update ScanIndel.py

modify parse_vaf function by calculating vaf using 1 - ( READref / READtotal ). I used this calculation rather than READalt / READtotal simply because there are cases (especially in microsatellite regions) where more than one alternate allele was detected at a given site in the same sample. Therefore, the variant allele fraction (or percent) shown is the total fraction for all variant alleles detected.