I am guessing that this isn't a bug you would report to the software developers at Duolingo but rather a typo (an extra space) that the Swahili course developers in Tanzania accidentally made.
The smartphone app has a free text field for reporting any kind of error in your own words. Strangely, the web version doesn't allow this. (Note that the app lacks the lesson tips and notes explaining the grammar of each topic. I now use both versions, to get the best of both worlds.)