fix the discrepancy of Ensembl fasta format naming convention

Ensembl changes the naming convention for the chromosome fasta files in the latest release by removing release number. For example, it was 'Homo_sapiens.GRCh37.74.dna.chromosome.N.fa.gz' for release 74, and 'Homo_sapiens.GRCh38.dna.chromosome.N.fa.gz' for release 76 and beyond. 

The following script takes care of this discrepancy.