submodule URLs change upstream and you need to update your local
repositories accordingly.
+
-"git submodule sync" synchronizes all submodules while
-"git submodule sync \-- A" synchronizes submodule "A" only.
+`git submodule sync` synchronizes all submodules while
+`git submodule sync -- A` synchronizes submodule "A" only.
+
If `--recursive` is specified, this command will recurse into the
registered submodules, and sync any nested submodules within.