fixed bug in _sort_releases()
fixed bug in _sort_releases()

Ensembl/ensembl,mjg17/ensembl,mjg17/ensembl,at7/ensembl,at7/ensembl,Ensembl/ensembl,Ensembl/ensembl,muffato/ensembl,muffato/ensembl,muffato/ensembl,danstaines/ensembl,james-monkeyshines/ensembl,james-monkeyshines/ensembl,mjg17/ensembl,danstaines/ensembl,danstaines/ensembl,james-monkeyshines/ensembl,muffato/ensembl,willmclaren/ensembl,willmclaren/ensembl,mjg17/ensembl,at7/ensembl,at7/ensembl,james-monkeyshines/ensembl,Ensembl/ensembl