x265: 2.6 -> 2.7

Semi-automatic update generated by https://github.com/ryantm/nix-update tools. These checks were done:

- built on NixOS
- ran `/nix/store/55ya7ybd3v04zyss7zc2dib0bk6xacxw-x265-2.7/bin/x265 -V` and found version 2.7
- ran `/nix/store/55ya7ybd3v04zyss7zc2dib0bk6xacxw-x265-2.7/bin/x265 --version` and found version 2.7
- found 2.7 with grep in /nix/store/55ya7ybd3v04zyss7zc2dib0bk6xacxw-x265-2.7
- found 2.7 in filename of file in /nix/store/55ya7ybd3v04zyss7zc2dib0bk6xacxw-x265-2.7