be consistent with the project style

Author: jzlxiaohei

src/createStore.js

@@ -62,8 +62,9 @@ export default function createStore(reducer, initialState) {
 
     return function unsubscribe() {
       var index = listeners.indexOf(listener);
-      if (index === -1)return;
-      listeners.splice(index, 1);
+      if (index !== -1) {
+        listeners.splice(index, 1);
+      }
     };
   }