Save settings when they are changed (#3743)

app/javascript/mastodon/actions/settings.js

@@ -3,10 +3,14 @@ import axios from 'axios';
 export const SETTING_CHANGE = 'SETTING_CHANGE';
 
 export function changeSetting(key, value) {
-  return {
+  return dispatch => {
+    dispatch({
       type: SETTING_CHANGE,
       key,
       value,
+    });
+
+    dispatch(saveSettings());
   };
 };