Update Gaia API documents for #1e41341d97efac2c303dced3dd0134999e008cb1
    Bug 958103 - [Messages][Drafts] Don't auto-save drafts when message input is empty

https://bugzilla.mozilla.org/show_bug.cgi?id=958103
Signed-off-by: Rick Waldron <waldron.rick@gmail.com>