Causes a continuous increase in memory usage

I am a Sketch Plug-in developer.

**Expected behavior:**

Sketch occupies almost no fluctuation in memory usage each time the plugin command containing `react-sketchapp` is called.

**Observed behavior:**

Each call to the command increases Sketch's non-recoverable memory footprint

**How to reproduce:**

See [antd-sketchapp](https://github.com/ant-design/antd-sketchapp/blob/master/docs/en-us/development.md#how-to-preview) demo.

**Sketch version:**

All versions.

**Please attach screenshots, a zip file of your project, and/or a link to your github project**


Start with the antd-sketchapp demo linked in the reproduction steps and run the Sketch plugin command repeatedly while monitoring Sketch's non-recoverable memory footprint. Trace the react-sketchapp command path from that demo; done means repeated calls no longer cause continuous memory growth across the reported Sketch versions.

Written by the indexing model from the issue text.