Support client builds in nix-shell --pure.

Dependencies

• [2] RFYEVKZQ Add nix-shell based build environment.

Change contents

• edit in shell.nix at line 19
  [2.99109]

  [2.99109]
  + pkgs.nodejs
• edit in shell.nix at line 21
  [2.99129]

  [2.99129]
  + pkgs.purescript
• edit in shell.nix at line 25
  [2.99207]

  [2.99207]
  +

  + shellHook = ''

  + export PATH="./node_modules/.bin:$PATH"

  + '';