[1.7.x] Fixed typo in squashing migrations documentation
[1.7.x] Fixed typo in squashing migrations documentation

Backport of af7d66b4f2 from master

oscaro/django,oscaro/django,jyotsna1820/django,oscaro/django,oscaro/django,jyotsna1820/django,jyotsna1820/django,jyotsna1820/django