python3.pkgs.pygmt: fix build by replacing invalid call to env.get

pkgs/development/python-modules/pygmt/default.nix

@@ -1,6 +1,5 @@
 {
   lib,
-  stdenv,
   pythonOlder,
   buildPythonPackage,
   fetchFromGitHub,
@@ -33,7 +32,7 @@ buildPythonPackage rec {
 
   postPatch = ''
     substituteInPlace pygmt/clib/loading.py \
-      --replace "env.get(\"GMT_LIBRARY_PATH\", \"\")" "env.get(\"GMT_LIBRARY_PATH\", \"${gmt}/lib\")"
+      --replace-fail "env.get(\"GMT_LIBRARY_PATH\")" "env.get(\"GMT_LIBRARY_PATH\", \"${gmt}/lib\")"
   '';
 
   nativeBuildInputs = [ setuptools-scm ];