Bump symfony/dom-crawler from 3.4.19 to 3.4.20 (#868)

Bumps [symfony/dom-crawler](https://github.com/symfony/dom-crawler) from 3.4.19 to 3.4.20.
<details>
<summary>Commits</summary>

- See full diff in [compare view](https://github.com/symfony/dom-crawler/compare/v3.4.19...v3.4.20)
</details>
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</details>

composer.lock

@@ -6860,7 +6860,7 @@
         },
         {
             "name": "symfony/dom-crawler",
-            "version": "v3.4.19",
+            "version": "v3.4.20",
             "source": {
                 "type": "git",
                 "url": "https://github.com/symfony/dom-crawler.git",