Update docs/adr/2022-03-23_018-single-state.md

Co-authored-by: Matthias Benkort <[email protected]>

docs/adr/2022-03-23_018-single-state.md

@@ -30,7 +30,7 @@ Draft
 * Given by the usage sites above, the `Hydra.Chain.Direct` module requires additional info to do both, construct protocol transactions with `postTx` as well as observe potential `OnChainTx` ([here](https://github.com/input-output-hk/hydra-poc/blob/a98e2907c4e425de2736782793383aad63132c14/hydra-node/src/Hydra/Chain/Direct.hs#L333-L336)). Hence we see that, operation of the `Hydra.Chain.Direct` component (and likely any implementing the interface fully) is **inherently stateful**.
 * We are looking at upcoming features to [handle rollbacks](https://github.com/input-output-hk/hydra-poc/issues/185) and dealing with [persisting the head state](https://github.com/input-output-hk/hydra-poc/issues/187).
   - Both could benefit from the idea, that the `HeadState` is just a result of pure `Event` processing (a.k.a event sourcing).
-  - Right now the `HeadState` kept in `Hydra.Node` alone, is not enough to do fully describe the state of the `hydra-node`. Hence it would not be enough to just persist all the `Event`s and replaying them to achieve persistence, nor resetting to some previous `HeadState` in the presence of a rollback.
+  - Right now the `HeadState` kept in `Hydra.Node` alone, is not enough to fully describe the state of the `hydra-node`. Hence it would not be enough to just persist all the `Event`s and replaying them to achieve persistence, nor resetting to some previous `HeadState` in the presence of a rollback.
 
 ## Decision