paperkey: fix tests

pkgs/tools/security/paperkey/default.nix

@@ -9,6 +9,13 @@ stdenv.mkDerivation rec {
     sha256 = "1prd2jaf4zjad3xhv160hmi5n408ssljfg7iz90jxs9w111pjwy4";
   };
 
+  postPatch = ''
+    for a in checks/*.sh ; do
+      substituteInPlace $a \
+        --replace /bin/echo echo
+    done
+  '';
+
   enableParallelBuilding = true;
 
   meta = with stdenv.lib; {