Cannot use [] for reading in

Prerequisites

[x] I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
[x] The issue still exists against the latest master branch of yii2-editors.
[x] This is not an usage question. I confirm having read the widget documentation and demos.
[x] This is not a general programming / coding question. (Those should be directed to the webtips Q & A forum).
[x] This is not a source plugin (summernote) issue. (Those should be directed to the plugin issues repo).
[x] I have attempted to find the simplest possible steps to reproduce the issue.
[ ] I have included a failing test as a pull request (Optional).

Steps to reproduce the issue

use PHP Version 5.6.40 on CentOS
use Demo of Summernote with model and activeform:

// Usage with ActiveForm and model and default settings echo $form->field($model, 'content')->widget(Summernote::class, [ 'options' => ['placeholder' => 'Edit your blog content here...'] ]);

Expected behavior and actual behavior

PHP Compile Error: yii\base\ErrorException - Cannot use [] for reading in /var/www/inwanet.inwatec.com/public_html/vendor/kartik-v/yii2-editors/src/assets/BaseAsset.php

Fix: change Line 27 in the above file from: $this->$ext[] = YII_DEBUG ? "{$file}.{$ext}" : "{$file}.min.{$ext}";

to: $this->{$ext}[] = YII_DEBUG ? "{$file}.{$ext}" : "{$file}.min.{$ext}";

Environment

Browsers

[ ] Google Chrome
[X] Mozilla Firefox
[ ] Internet Explorer
[ ] Safari

Operating System

[ ] Windows
[ ] Mac OS X
[x] Linux
[ ] Mobile

Libraries

jQuery version: 2.2.4
yii2-editors version: 1.0.1

Isolating the problem

[ ] This bug happens on the widget demos page
[x] The bug happens consistently across all tested browsers
[X] This bug happens when using yii2-editors without other plugins
[ ] I can reproduce this bug in a jsbin

kartik-v / yii2-editors