Minor language fixes. (#818)

* Typo fix in "Mutations" section.

Fixed via rephrasing slightly.

* Typo fix in "Actions" section.

* Typo fix in "Modules" section.

Author: Francisc

docs/en/actions.md

@@ -1,6 +1,6 @@
 # Actions
 
-Actions are similar to mutations, the difference being that:
+Actions are similar to mutations, the differences being that:
 
 - Instead of mutating the state, actions commit mutations.
 - Actions can contain arbitrary asynchronous operations.

docs/en/modules.md

@@ -248,7 +248,7 @@ You can also remove a dynamically registered module with `store.unregisterModule
 
 Sometimes we may need to create multiple instances of a module, for example:
 
-- Creating multiple stores that uses the same module (e.g. To [avoid stateful singletons in the SSR](https://ssr.vuejs.org/en/structure.html#avoid-stateful-singletons) when the `runInNewContext` option is `false` or `'once'`);
+- Creating multiple stores that use the same module (e.g. To [avoid stateful singletons in the SSR](https://ssr.vuejs.org/en/structure.html#avoid-stateful-singletons) when the `runInNewContext` option is `false` or `'once'`);
 - Register the same module multiple times in the same store.
 
 If we use a plain object to declare the state of the module, then that state object will be shared by reference and cause cross store/module state pollution when it's mutated.

docs/en/mutations.md

@@ -16,7 +16,7 @@ const store = new Vuex.Store({
 })
 ```
 
-You cannot directly call a mutation handler. The options here is more like event registration: "When a mutation with type `increment` is triggered, call this handler." To invoke a mutation handler, you need to call `store.commit` with its type:
+You cannot directly call a mutation handler. Think of it more like event registration: "When a mutation with type `increment` is triggered, call this handler." To invoke a mutation handler, you need to call `store.commit` with its type:
 
 ``` js
 store.commit('increment')