chore(gh): update mkdocs-open-in-new-tab requirement from >=1.0.3 to >=1.0.8 (#283)

Updates the requirements on
[mkdocs-open-in-new-tab](https://github.com/JakubAndrysek/mkdocs-open-in-new-tab)
to permit the latest version.
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Author: nathanthaler

docs/requirements.txt

@@ -1,4 +1,4 @@
 mkdocs-git-revision-date-localized-plugin >= 1.2.2
 mkdocs-markdownextradata-plugin >= 0.2.5
 mkdocs-minify-plugin>=0.7.2
-mkdocs-open-in-new-tab>=1.0.3
+mkdocs-open-in-new-tab>=1.0.8