flake.lock: Update (#116)

Flake lock file updates:

• Updated input 'flake-utils':
    'github:numtide/flake-utils/04c1b180862888302ddfb2e3ad9eaa63afc60cf8' (2022-05-17)
  → 'github:numtide/flake-utils/1ed9fb1935d260de5fe1c2f7ee0ebaae17ed2fa1' (2022-05-30)
• Updated input 'nixpkgs':
    'github:nixos/nixpkgs/dfd82985c273aac6eced03625f454b334daae2e8' (2022-05-20)
  → 'github:nixos/nixpkgs/90cd5459a1fd707819b9a3fb9c852beaaac3b79a' (2022-06-11)
• Updated input 'rust-overlay':
    'github:oxalica/rust-overlay/86cc394cd4d5eb7a85749677de297cb9eb33664c' (2022-05-22)
  → 'github:oxalica/rust-overlay/e04a88d7f859ae9ec42267866bb68c1a741e6859' (2022-06-12)

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