[1.8.x] Minor edits to docs/ref/forms/validation.txt
[1.8.x] Minor edits to docs/ref/forms/validation.txt

Backport of 73b5b0b4a5989f159c6dadcb670ab30b01402382 from master

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