Use “their” instead of “his” (#1360)

Use “their” instead of “his”

book/05-distributed-git/sections/distributed-workflows.asc

@@ -67,7 +67,7 @@ This is a variant of a multiple-repository workflow.
 It's generally used by huge projects with hundreds of collaborators; one famous example is the Linux kernel.
 Various integration managers are in charge of certain parts of the repository; they're called _lieutenants_.
 All the lieutenants have one integration manager known as the benevolent dictator.
-The benevolent dictator pushes from his directory to a reference repository from which all the collaborators need to pull.
+The benevolent dictator pushes from their directory to a reference repository from which all the collaborators need to pull.
 The process works like this (see <<wfdiag_c>>):
 
 1.  Regular developers work on their topic branch and rebase their work on top of `master`.

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

@@ -376,7 +376,7 @@ Submodule DbConnector c3f01dc..c87d55d:
 Git will by default try to update *all* of your submodules when you run `git submodule update --remote` so if you have a lot of them, you may want to pass the name of just the submodule you want to try to update.
 
 ===== Pulling Upstream Changes from the Project Remote
-Let's now step into the shoes of your collaborator, who has his own local clone of the MainProject repository.
+Let's now step into the shoes of your collaborator, who has their own local clone of the MainProject repository.
 Simply executing `git pull` to get your newly committed changes is not enough:
 
 [source,console]