docs: fix some language issues and deprecated link (#3733)

docs/spec/abci/abci.md

@@ -141,7 +141,7 @@ on them. All other fields in the `Response*` must be strictly deterministic.
 ## Block Execution
 
 The first time a new blockchain is started, Tendermint calls
-`InitChain`. From then on, the follow sequence of methods is executed for each
+`InitChain`. From then on, the following sequence of methods is executed for each
 block:
 
 `BeginBlock, [DeliverTx], EndBlock, Commit`

docs/spec/blockchain/encoding.md

@@ -218,7 +218,7 @@ func MerkleRoot(items [][]byte) []byte{
 	case 0:
 		return nil
 	case 1:
-		return leafHash(leafs[0])
+		return leafHash(items[0])
 	default:
 		k := getSplitPoint(len(items))
 		left := MerkleRoot(items[:k])

docs/spec/blockchain/state.md

@@ -59,7 +59,7 @@ type Validator struct {
 When hashing the Validator struct, the address is not included,
 because it is redundant with the pubkey.
 
-The `state.Validators`, `state.LastValidators`, and `state.NextValidators`, must always by sorted by validator address,
+The `state.Validators`, `state.LastValidators`, and `state.NextValidators`, must always be sorted by validator address,
 so that there is a canonical order for computing the MerkleRoot.
 
 We also define a `TotalVotingPower` function, to return the total voting power: