git-fire: set meta.mainProgram

pkgs/tools/misc/git-fire/default.nix

@@ -25,6 +25,7 @@ stdenv.mkDerivation {
     homepage = "https://github.com/qw3rtman/git-fire";
     license = licenses.mit;
     platforms = platforms.all;
-    maintainers = [ maintainers.swflint ];
+    maintainers = with maintainers; [ swflint ];
+    mainProgram = "git-fire";
   };
 }