deer: simpler perl patch

pkgs/shells/zsh-deer/default.nix

@@ -14,9 +14,8 @@ in stdenv.mkDerivation {
   };
 
   prePatch = ''
-    sed -i '157s/perl/'\
-    "$(echo ${perl}/bin/perl | sed 's/\//\\\//g')"'/' \
-    deer
+    substituteInPlace deer \
+      --replace " perl " " ${perl}/bin/perl "
   '';
 
   patches = [ ./realpath.patch ];