Update verbiage for spec/01-state.md

Co-authored-by: John Letey <john@nobleassets.xyz>
Signed-off-by: Julian Kocher <kocherju@gmail.com>

spec/01-state.md

@@ -30,7 +30,7 @@ The `ForwardingAccount` structure stores the data needed for forwarding. This in
 - **BaseAccount**: inherits from `cosmos.auth.v1beta1.BaseAccount`
 - **channel**: specifies the IBC channel through which tokens are forwarded
 - **recipient**: the address that receives the forwarded tokens
-- **created_at**: timestamp at creation
+- **created_at**: block height at creation
 - **fallback**: a fallback address to be used if forwarding to the primary recipient fails
 
 #### State Update