Fix typos in foreign key docs
Fix typos in foreign key docs

These slipped in as part of #1156
carragom/knex,noodle/knex,joeframbach/knex,harriha/knex,WaltRock/knex,whitelynx/knex,wubzz/knex,harriha/knex,carragom/knex,joeframbach/knex,statyan/knex,Atlantis-Software/knex,whitelynx/knex,vellotis/knex,maxcnunes/knex,CorvusCorrax/knex,tgriesser/knex,maxcnunes/knex,noodle/knex,WaltRock/knex,tgriesser/knex,tgriesser/knex,joeframbach/knex,vellotis/knex,Atlantis-Software/knex,vellotis/knex,whitelynx/knex,wubzz/knex,abegines/knex,CorvusCorrax/knex,maxcnunes/knex,abegines/knex,harriha/knex,statyan/knex