Add latest audit to repository (#1664)

* rename previous audit to date it was performed

* add latest audit

* add note about latest audit in README

README.md

@@ -38,6 +38,8 @@ OpenZeppelin the project is maintained by [Zeppelin] the company, and developed
 
 The core development principles and strategies that OpenZeppelin is based on include: security in depth, simple and modular code, clarity-driven naming conventions, comprehensive unit testing, pre-and-post-condition sanity checks, code consistency, and regular audits.
 
+The latest audit was done on October 2018 on version 2.0.0.
+
 Please report any security issues you find to security@openzeppelin.org.
 
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