gatling: 0.13 -> 0.15

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

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

These checks were done:

- built on NixOS
- ran `/nix/store/l781ikxl4sjd90dkwylgyvyz53lyn5vm-gatling-0.15/bin/gatling -h` got 0 exit code
- ran `/nix/store/l781ikxl4sjd90dkwylgyvyz53lyn5vm-gatling-0.15/bin/gatling --help` got 0 exit code
- ran `/nix/store/l781ikxl4sjd90dkwylgyvyz53lyn5vm-gatling-0.15/bin/gatling --version` and found version 0.15
- ran `/nix/store/l781ikxl4sjd90dkwylgyvyz53lyn5vm-gatling-0.15/bin/gatling --help` and found version 0.15
- ran `/nix/store/l781ikxl4sjd90dkwylgyvyz53lyn5vm-gatling-0.15/bin/dl -h` got 0 exit code
- ran `/nix/store/l781ikxl4sjd90dkwylgyvyz53lyn5vm-gatling-0.15/bin/dl --help` got 0 exit code
- ran `/nix/store/l781ikxl4sjd90dkwylgyvyz53lyn5vm-gatling-0.15/bin/dl help` got 0 exit code
- ran `/nix/store/l781ikxl4sjd90dkwylgyvyz53lyn5vm-gatling-0.15/bin/dl -V` and found version 0.15
- ran `/nix/store/l781ikxl4sjd90dkwylgyvyz53lyn5vm-gatling-0.15/bin/dl --version` and found version 0.15
- ran `/nix/store/l781ikxl4sjd90dkwylgyvyz53lyn5vm-gatling-0.15/bin/dl -h` and found version 0.15
- ran `/nix/store/l781ikxl4sjd90dkwylgyvyz53lyn5vm-gatling-0.15/bin/dl --help` and found version 0.15
- ran `/nix/store/l781ikxl4sjd90dkwylgyvyz53lyn5vm-gatling-0.15/bin/getlinks -h` got 0 exit code
- ran `/nix/store/l781ikxl4sjd90dkwylgyvyz53lyn5vm-gatling-0.15/bin/getlinks --help` got 0 exit code
- ran `/nix/store/l781ikxl4sjd90dkwylgyvyz53lyn5vm-gatling-0.15/bin/getlinks help` got 0 exit code
- found 0.15 with grep in /nix/store/l781ikxl4sjd90dkwylgyvyz53lyn5vm-gatling-0.15
- directory tree listing: https://gist.github.com/d54dd9d5cdf367db1648e6719090a75d