Update src/api.md

Co-authored-by: Pierre Krieger <pierre.krieger1708@gmail.com>

Author: josepot

src/api.md

@@ -8,4 +8,4 @@ Any missing parameter, or parameter with an invalid format, should result in a J
 
 - "hexadecimal-encoded" designates a binary value encoded as hexadecimal. The value must either be empty, or start with `"0x"` and contain an even number of characters.
 - "SCALE-encoded" designates a value encoded using [the SCALE codec](https://docs.substrate.io/v3/advanced/scale-codec/).
-- "Merkle value" as decribed in the [Polkadot spec](https://spec.polkadot.network/chap-state#defn-merkle-value).
+- "Merkle value" is described in the [Polkadot specification](https://spec.polkadot.network/chap-state#defn-merkle-value).