Apply suggestion to doc/administration/git_annex.md

doc/administration/git_annex.md

@@ -9,7 +9,7 @@ removed](https://gitlab.com/gitlab-org/gitlab/issues/1648) in GitLab 9.0 (2017/0
 Read through the [migration guide from git-annex to Git LFS](../topics/git/lfs/migrate_from_git_annex_to_git_lfs.md).
 
 The biggest limitation of Git, compared to some older centralized version
-control systems have been the maximum size of the repositories.
+control systems has been the maximum size of the repositories.
 
 The general recommendation is to not have Git repositories larger than 1GB to
 preserve performance. Although GitLab has no limit (some repositories in GitLab