Update security.md

Hi Guys 
I was reading through this guide last night and noticed a small mistake, would be great if you could update it. 
I changed the word 'building' to 'build' in line 20. 
"Web application frameworks are made to help developers building web applications"
test cases to describe the MySQL boolean behavior.
Unifies mysql and mysql2 casting of booleans.
Merge pull request #12425 from senny/mysql_booleans

Unify boolean quoting for Mysql- and Mysql2Adapter.
Merge pull request #12815 from Adam89/patch-1

Update security.md [ci skip]
Do not decrement counter_cache if has_many_through_association destroyed using :destroy method which has own counter_cache callbacks, fixes #11079