setup-msysgit: avoid using the dashed form

It has been deprecated for quite a while now...

Besides, it does not seem to work here:
ln: accessing `//installer-tmp/bin/git.exe': No such host or network path
ln: accessing `//installer-tmp/bin/git.exe': No such host or network path
...

share/msysGit/net/setup-msysgit.sh

@@ -77,7 +77,7 @@ echo
 echo -------------------------------------------------------
 echo Checking out the msysgit @@MSYSGITBRANCH@@ branch
 echo -------------------------------------------------------
-git-checkout -l -f -q -b @@MSYSGITBRANCH@@ origin/@@MSYSGITBRANCH@@ ||
+git checkout -l -f -q -b @@MSYSGITBRANCH@@ origin/@@MSYSGITBRANCH@@ ||
 	error Couldn\'t checkout the @@MSYSGITBRANCH@@ branch!
 mkdir -p .git/hooks &&
 cp share/msysGit/post-checkout-hook .git/hooks/post-checkout ||
@@ -167,7 +167,7 @@ git init &&
 git config remote.origin.url $GITCHEETAH_REPO_URL &&
 git config remote.origin.fetch '+refs/heads/*:refs/remotes/origin/*' &&
 git fetch origin &&
-git-checkout -l -f -q -b master origin/master ||
+git checkout -l -f -q -b master origin/master ||
 	error "Could not update the submodule src/git-cheetah!"
 
 # Copy profile.d/*.sh if there is any