Submodules: fix grammar as suggested by Ben

See progit/progit2#1368 (comment)

Co-Authored-By: Ben Straub <[email protected]>

Author: phil-blain

book/07-git-tools/sections/submodules.asc

@@ -437,7 +437,7 @@ This will make Git run `git submodule update` right after the pull, putting the
 Moreover, if you want to make Git always pull with `--recurse-submodules`, you can set the configuration option `submodule.recurse` to true (this works for `git pull` since Git 2.15).
 This option will make Git use the `--recurse-submodules` flag for all commands that support it (except `clone`).
 
-There is a special situation that can happen when pulling superproject updates : maybe the upstream repository changes the URL of the submodule in the `.gitmodules` file in one of the commits you pull.
+There is a special situation that can happen when pulling superproject updates: it could be that the upstream repository has changed the URL of the submodule in the `.gitmodules` file in one of the commits you pull.
 This can happen for example if the submodule project changes its hosting platform.
 In that case, it is possible for `git pull --recurse-submodules`, or `git submodule update`, to fail if the superproject references a submodule commit that is not found in the submodule remote locally configured in your repository.
 In order to remedy this situation, the `git submodule sync` command is required: