postman: fix passing args in darwin app wrapper

Due to incorrect escaping, the wrapper script on Darwin currently bakes
in "installerPhase" rather than "$@". Postman doesn't really seem to do
anything with cli args as far as I can tell, but fixing this aligns it
better with other packages that also provide app wrappers on Darwin.

pkgs/by-name/po/postman/darwin.nix

@@ -50,7 +50,7 @@ stdenvNoCC.mkDerivation {
     cp -R . $out/Applications/${appName}
     cat > $out/bin/${pname} << EOF
     #!${stdenvNoCC.shell}
-    open -na $out/Applications/${appName} --args "$@"
+    open -na $out/Applications/${appName} --args "\$@"
     EOF
     chmod +x $out/bin/${pname}
     runHook postInstall