environment: clear up activationScript creation

modules/home-environment.nix

@@ -389,7 +389,7 @@ in
             abort ("Dependency cycle in activation script: "
               + builtins.toJSON sortedCommands);
 
-        sf = pkgs.writeText "activation-script" ''
+        activationScript = pkgs.writeScript "activation-script" ''
           #!${pkgs.stdenv.shell}
 
           set -eu
@@ -434,7 +434,7 @@ in
           phases = [ "installPhase" ];
 
           installPhase = ''
-            install -D -m755 ${sf} $out/activate
+            install -D ${activationScript} $out/activate
 
             substituteInPlace $out/activate \
               --subst-var-by GENERATION_DIR $out