Fix call to update_imap_flags in order to properly set is_draft attribute.
Fix call to update_imap_flags in order to properly set is_draft attribute.

Gmail uses a '\\Draft` *label*, not the '\\Draft' IMAP flag, so by omitting
that second parameter we weren't marking synced drafts as such.

nylas/sync-engine,jobscore/sync-engine,ErinCall/sync-engine,Eagles2F/sync-engine,Eagles2F/sync-engine,wakermahmud/sync-engine,nylas/sync-engine,ErinCall/sync-engine,EthanBlackburn/sync-engine,closeio/nylas,jobscore/sync-engine,wakermahmud/sync-engine,nylas/sync-engine,gale320/sync-engine,EthanBlackburn/sync-engine,jobscore/sync-engine,ErinCall/sync-engine,closeio/nylas,wakermahmud/sync-engine,PriviPK/privipk-sync-engine,PriviPK/privipk-sync-engine,jobscore/sync-engine,nylas/sync-engine,wakermahmud/sync-engine,ErinCall/sync-engine,Eagles2F/sync-engine,ErinCall/sync-engine,closeio/nylas,Eagles2F/sync-engine,Eagles2F/sync-engine,EthanBlackburn/sync-engine,wakermahmud/sync-engine,EthanBlackburn/sync-engine,PriviPK/privipk-sync-engine,PriviPK/privipk-sync-engine,gale320/sync-engine,EthanBlackburn/sync-engine,gale320/sync-engine,gale320/sync-engine,closeio/nylas,PriviPK/privipk-sync-engine,gale320/sync-engine