Update access-control.adoc (#1837)

Update URL to openzeppelin.com

docs/modules/ROOT/pages/access-control.adoc

@@ -1,6 +1,6 @@
 = Access Control
 
-Access control—that is, "who is allowed to do this thing"—is incredibly important in the world of smart contracts. The access control of your contract may govern who can mint tokens, vote on proposals, freeze transfers, and many others. It is therefore critical to understand how you implement it, lest someone else https://blog.zeppelin.solutions/on-the-parity-wallet-multisig-hack-405a8c12e8f7[steals your whole system].
+Access control—that is, "who is allowed to do this thing"—is incredibly important in the world of smart contracts. The access control of your contract may govern who can mint tokens, vote on proposals, freeze transfers, and many others. It is therefore critical to understand how you implement it, lest someone else https://blog.openzeppelin.com/on-the-parity-wallet-multisig-hack-405a8c12e8f7[steals your whole system].
 
 [[ownership-and-ownable]]
 == Ownership and `Ownable`