Doc link fixes (#4116)

- closes #4090
- closes #4091

Signed-off-by: Marko Baricevic <marbar3778@yahoo.com>

docs/app-dev/app-architecture.md

@@ -51,4 +51,4 @@ See the following for more extensive documentation:
 - [Interchain Standard for the Light-Client REST API](https://github.com/cosmos/cosmos-sdk/pull/1028)
 - [Tendermint RPC Docs](https://tendermint.com/rpc/)
 - [Tendermint in Production](../tendermint-core/running-in-production.md)
-- [ABCI spec](./abci-spec.md)
+- [ABCI spec](https://github.com/tendermint/spec/tree/95cf253b6df623066ff7cd4074a94e7a3f147c7a/spec/abci)

docs/spec/blockchain/encoding.md

@@ -296,7 +296,7 @@ conceivable purpose.
 
 ### IAVL+ Tree
 
-Because Tendermint only uses a Simple Merkle Tree, application developers are expect to use their own Merkle tree in their applications. For example, the IAVL+ Tree - an immutable self-balancing binary tree for persisting application state is used by the [Cosmos SDK](https://github.com/cosmos/cosmos-sdk/blob/master/docs/clients/lite/specification.md)
+Because Tendermint only uses a Simple Merkle Tree, application developers are expect to use their own Merkle tree in their applications. For example, the IAVL+ Tree - an immutable self-balancing binary tree for persisting application state is used by the [Cosmos SDK](https://github.com/cosmos/cosmos-sdk/blob/ae77f0080a724b159233bd9b289b2e91c0de21b5/docs/interfaces/lite/specification.md)
 
 ## JSON