flake.lock: Update

Flake input changes:

  • Updated 'nix': 'github:NixOS/nix/8b4a542d1767e0df7b3c0902b766f34352cb0958' -> 'github:NixOS/nix/20a7d8d23a19530207378fc74ddd558232240f43'
  • Updated 'nix/nixpkgs': 'github:NixOS/nixpkgs/70717a337f7ae4e486ba71a500367cad697e5f09' -> 'github:NixOS/nixpkgs/3a10a004bb5802d5f23c58886722e4239705e733'

Created by  Eelco Dolstra  on October 18, 2020
HWICNB75QGCKT2RU4WNR3WF2WYQYI5F6J5PVBT4TYTOFSLBGGCVQC
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