Typo fixes

doc/raketasks/cleanup.md

-### Remove grabage from filesystem. Important! Data loss!
-Remove namespaces(dirs) from /home/git/repositories if they dont exist in GitLab database
+### Remove garbage from filesystem. Important! Data loss!
+Remove namespaces(dirs) from `/home/git/repositories` if they don't exist in GitLab database.
 ```
 bundle exec rake gitlab:cleanup:dirs RAILS_ENV=production
 ```
-Remove repositories (global only for now) from /home/git/repositories if they dont exist in GitLab database
+Remove repositories (global only for now) from `/home/git/repositories` if they don't exist in GitLab database.
 ```
 bundle exec rake gitlab:cleanup:repos RAILS_ENV=production