electrum-ltc: 3.0.6.2 -> 3.1.2.1

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

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

These checks were done:

- built on NixOS
- ran `/nix/store/01743lqqy8qxmygc7rk86h14089v8ijx-electrum-ltc-3.1.2.1/bin/.electrum-ltc-wrapped -h` got 0 exit code
- ran `/nix/store/01743lqqy8qxmygc7rk86h14089v8ijx-electrum-ltc-3.1.2.1/bin/.electrum-ltc-wrapped --help` got 0 exit code
- ran `/nix/store/01743lqqy8qxmygc7rk86h14089v8ijx-electrum-ltc-3.1.2.1/bin/.electrum-ltc-wrapped help` got 0 exit code
- ran `/nix/store/01743lqqy8qxmygc7rk86h14089v8ijx-electrum-ltc-3.1.2.1/bin/electrum-ltc -h` got 0 exit code
- ran `/nix/store/01743lqqy8qxmygc7rk86h14089v8ijx-electrum-ltc-3.1.2.1/bin/electrum-ltc --help` got 0 exit code
- ran `/nix/store/01743lqqy8qxmygc7rk86h14089v8ijx-electrum-ltc-3.1.2.1/bin/electrum-ltc help` got 0 exit code
- found 3.1.2.1 with grep in /nix/store/01743lqqy8qxmygc7rk86h14089v8ijx-electrum-ltc-3.1.2.1
- directory tree listing: https://gist.github.com/7bdf4bff59f77c44f7aa7a0cddfb60b7