flake.lock: Update (#3930)

Flake lock file updates:

• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/710fed5a2483f945b14f4a58af2cd3676b42d8c8' (2022-03-30)
  → 'github:NixOS/nixpkgs/42948b300670223ca8286aaf916bc381f66a5313' (2022-04-08)
• Updated input 'pre-commit-hooks':
    'github:cachix/pre-commit-hooks.nix/b6bc0b21e1617e2b07d8205e7fae7224036dfa4b' (2022-03-01)
  → 'github:cachix/pre-commit-hooks.nix/e5e7b3b542e7f4f96967966a943d7e1c07558042' (2022-04-04)
• Updated input 'rust-overlay':
    'github:oxalica/rust-overlay/7c90e17cd7c0b9e81d5b23f78b482088ac9961d1' (2022-04-02)
  → 'github:oxalica/rust-overlay/4579190c4c427b8350c662417c26254589dfe658' (2022-04-09)

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]