Make the backup Rake task the same as in EE
Make the backup Rake task the same as in EE

EE uses single quotes for the changed line, whereas CE was using double
quotes. This commit ensures both repositories use the same kind of
quotes.

mmkassem/gitlabhq,stoplightio/gitlabhq,iiet/iiet-git,stoplightio/gitlabhq,mmkassem/gitlabhq,mmkassem/gitlabhq,iiet/iiet-git,iiet/iiet-git,mmkassem/gitlabhq,iiet/iiet-git,stoplightio/gitlabhq,stoplightio/gitlabhq