shmig: fix `migrate` command when postgres is enabled

pkgs/development/tools/database/shmig/default.nix

@@ -1,6 +1,6 @@
 { stdenv, fetchFromGitHub
 , withMySQL ? true, withPSQL ? false, withSQLite ? false
-, mysql, postgresql, sqlite, gawk
+, mysql, postgresql, sqlite, gawk, gnugrep, findutils, gnused
 , lib
 }:
 
@@ -24,7 +24,10 @@ stdenv.mkDerivation rec {
       --replace "\`which mysql\`" "${lib.optionalString withMySQL "${mysql.client}/bin/mysql"}" \
       --replace "\`which psql\`" "${lib.optionalString withPSQL "${postgresql}/bin/psql"}" \
       --replace "\`which sqlite3\`" "${lib.optionalString withSQLite "${sqlite}/bin/sqlite3"}" \
-      --replace "awk" "${gawk}/bin/awk"
+      --replace "awk" "${gawk}/bin/awk" \
+      --replace "grep" "${gnugrep}/bin/grep" \
+      --replace "find" "${findutils}/bin/find" \
+      --replace "sed" "${gnused}/bin/sed"
   '';
 
   preBuild = ''