applgrid: move gfortran to nativeBuildInputs

pkgs/development/libraries/physics/applgrid/default.nix

···
     sha256 = "1yw9wrk3vjv84kd3j4s1scfhinirknwk6xq0hvj7x2srx3h93q9p";
   };
 
+  nativeBuildInputs = [ gfortran ];
+
   # For some reason zlib was only needed after bump to gfortran8
-  buildInputs = [ gfortran hoppet lhapdf root5 zlib ];
+  buildInputs = [ hoppet lhapdf root5 zlib ];
 
   patches = [
     ./bad_code.patch