samtools: 1.7 -> 1.8

Semi-automatic update generated by https://github.com/ryantm/nixpkgs-update tools.

This update was made based on information from https://repology.org/metapackage/samtools/versions.

These checks were done:

- built on NixOS
- ran ‘/nix/store/ip1zr4rg4pwq8f3fs8ar570l0zdicai7-samtools-1.8/bin/samtools --help’ got 0 exit code
- ran ‘/nix/store/ip1zr4rg4pwq8f3fs8ar570l0zdicai7-samtools-1.8/bin/samtools help’ got 0 exit code
- ran ‘/nix/store/ip1zr4rg4pwq8f3fs8ar570l0zdicai7-samtools-1.8/bin/blast2sam.pl -h’ got 0 exit code
- ran ‘/nix/store/ip1zr4rg4pwq8f3fs8ar570l0zdicai7-samtools-1.8/bin/blast2sam.pl --help’ got 0 exit code
- ran ‘/nix/store/ip1zr4rg4pwq8f3fs8ar570l0zdicai7-samtools-1.8/bin/blast2sam.pl help’ got 0 exit code
- ran ‘/nix/store/ip1zr4rg4pwq8f3fs8ar570l0zdicai7-samtools-1.8/bin/novo2sam.pl help’ got 0 exit code
- ran ‘/nix/store/ip1zr4rg4pwq8f3fs8ar570l0zdicai7-samtools-1.8/bin/psl2sam.pl -h’ got 0 exit code
- ran ‘/nix/store/ip1zr4rg4pwq8f3fs8ar570l0zdicai7-samtools-1.8/bin/psl2sam.pl --help’ got 0 exit code
- ran ‘/nix/store/ip1zr4rg4pwq8f3fs8ar570l0zdicai7-samtools-1.8/bin/psl2sam.pl help’ got 0 exit code
- ran ‘/nix/store/ip1zr4rg4pwq8f3fs8ar570l0zdicai7-samtools-1.8/bin/soap2sam.pl -h’ got 0 exit code
- ran ‘/nix/store/ip1zr4rg4pwq8f3fs8ar570l0zdicai7-samtools-1.8/bin/soap2sam.pl --help’ got 0 exit code
- ran ‘/nix/store/ip1zr4rg4pwq8f3fs8ar570l0zdicai7-samtools-1.8/bin/soap2sam.pl help’ got 0 exit code
- found 1.8 with grep in /nix/store/ip1zr4rg4pwq8f3fs8ar570l0zdicai7-samtools-1.8
- directory tree listing: https://gist.github.com/4673ea3645eb509035dcb386c4ad1da2