[1.8.x] Fixed typos in docs/ref/forms/fields.txt
[1.8.x] Fixed typos in docs/ref/forms/fields.txt

Backport of a6b77abff75709ee09a0d31d450af601f1f806d9 from master

h4r5h1t/django-hauthy,pquentin/django,h4r5h1t/django-hauthy,h4r5h1t/django-hauthy,h4r5h1t/django-hauthy,pquentin/django,pquentin/django