docs: fix typo in mutations.md (#2066)

Author: idorenyinudoh

docs/guide/mutations.md

@@ -137,7 +137,7 @@ mutations: {
 }
 ```
 
-Now imagine we are debugging the app and looking at the devtool's mutation logs. For every mutation logged, the devtool will need to capture a "before" and "after" snapshots of the state. However, the asynchronous callback inside the example mutation above makes that impossible: the callback is not called yet when the mutation is committed, and there's no way for the devtool to know when the callback will actually be called - any state mutation performed in the callback is essentially un-trackable!
+Now imagine we are debugging the app and looking at the devtool's mutation logs. For every mutation logged, the devtool will need to capture a "before" and "after" snapshot of the state. However, the asynchronous callback inside the example mutation above makes that impossible: the callback is not called yet when the mutation is committed, and there's no way for the devtool to know when the callback will actually be called - any state mutation performed in the callback is essentially un-trackable!
 
 ## Committing Mutations in Components