Auto merge of #2691 - rust-lang:renovate/ember-source-3.20.x, r=Turbo87

Update dependency ember-source to v3.20.4

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [ember-source](https://emberjs.com/) ([source](https://togithub.com/emberjs/ember.js)) | devDependencies | patch | [`3.20.3` -> `3.20.4`](https://renovatebot.com/diffs/npm/ember-source/3.20.3/3.20.4) |

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### Release Notes

<details>
<summary>emberjs/ember.js</summary>

### [`v3.20.4`](https://togithub.com/emberjs/ember.js/blob/master/CHANGELOG.md#v3204-August-11-2020)

[Compare Source](https://togithub.com/emberjs/ember.js/compare/v3.20.3...v3.20.4)

-   [#&#8203;19047](https://togithub.com/emberjs/ember.js/pull/19047) Ensure `inject-babel-helpers` plugin can be parallelized
-   [#&#8203;19089](https://togithub.com/emberjs/ember.js/pull/19089) Update rendering engine to improve immediate encoding performance
-   [#&#8203;19082](https://togithub.com/emberjs/ember.js/pull/19082) Simplify mixin application
-   [#&#8203;19088](https://togithub.com/emberjs/ember.js/pull/19088) Simplify factory instantiation from the container
-   [#&#8203;19028](https://togithub.com/emberjs/ember.js/pull/19028) Ensure setter CP's with dependent keys on curly components can be two way bound
-   [#&#8203;19077](https://togithub.com/emberjs/ember.js/pull/19077) Simplify `get` and improve `computed` caching scheme.
-   [#&#8203;19065](https://togithub.com/emberjs/ember.js/pull/19065) / [#&#8203;19072](https://togithub.com/emberjs/ember.js/pull/19072) - Updates GlimmerVM to improve internal destroyable system and improve tag / revision computation.
-   [#&#8203;19081](https://togithub.com/emberjs/ember.js/pull/19081) Reduces template compilation size in production builds.

</details>

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Author: bors

package-lock.json

@@ -87,7 +87,7 @@
     "ember-qunit": "4.6.0",
     "ember-resolver": "8.0.2",
     "ember-router-scroll": "2.0.2",
-    "ember-source": "3.20.3",
+    "ember-source": "3.20.4",
     "ember-svg-jar": "2.2.3",
     "ember-template-lint": "2.10.0",
     "ember-test-selectors": "4.1.0",