memo: refactoring dependency paths

pkgs/applications/misc/memo/default.nix

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-{ fetchFromGitHub, ack , tree, stdenv, ... }:
+{ fetchFromGitHub, ag, tree, stdenv, ... }:
 
 stdenv.mkDerivation rec {
 
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   installPhase = ''
     mkdir -p $out/{bin,share/man/man1,share/bash-completion/completions}
+    substituteInPlace memo \
+      --replace "ack "  "${ag}/bin/ag " \
+      --replace "tree " "${tree}/bin/tree "
     mv memo $out/bin/
     mv doc/memo.1 $out/share/man/man1/memo.1
     mv completion/memo.bash $out/share/bash-completion/completions/memo.sh
···
     maintainers = [ stdenv.lib.maintainers.mrVanDalo ];
     platforms = stdenv.lib.platforms.all;
   };
-}
+}