[1.5.x] Fixed #21218 -- Typo on docs/howto/upgrade-version.txt
[1.5.x] Fixed #21218 -- Typo on docs/howto/upgrade-version.txt

Thanks ryan at ryangallen.com for the report.

Backport of 36e220f923 from master

bliti/django-nonrel-1.5,ccn-2m/django,ccn-2m/django,ccn-2m/django,bliti/django-nonrel-1.5,ccn-2m/django,bliti/django-nonrel-1.5