flake.lock: Update

Flake input changes:

  • Updated 'nix': 'github:NixOS/nix/1ab9da915422405452118ebb17b88cdfc90b1e10' -> 'github:NixOS/nix/d7c0f094cbcfe1ae4ccc3d54baec00b66ccb1ed0'

Created by  Eelco Dolstra  on July 27, 2020
MXK3N5OHR3TPW76VZLPTXK3RBM5YDQLJIPDR6G5EELFQROOFDHKQC
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