Update basic_associations.md

Update assignment due to changes in the Rails Guide

ruby_on_rails/active_record_basics/basic_associations.md

@@ -68,7 +68,7 @@ If you're a normal human, you're probably somewhere between "huh?" and "I hate y
 
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-1. Read the beginning of the [Rails Guides Associations Chapter](http://guides.rubyonrails.org/association_basics.html), just up until section 2.7. Everything after that we can save for later... the important thing is that you've seen the relationships and how they're set up.
+1. Read the beginning of the [Rails Guides Associations Chapter](http://guides.rubyonrails.org/association_basics.html), just up until section 2.6.1.5. Everything after that we can save for later... the important thing is that you've seen the relationships and how they're set up.
 
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