bug #29 Fix data-theme attribut (cedriclombardot)

This PR was merged into the main branch.

Discussion
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Fix data-theme attribut

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| Tickets       |
| License       | MIT

hasAttribute return a boolean not attribute value

Commits
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9d9b593 Fix data-theme attribut

Author: tgalopin

src/Swup/Resources/assets/src/controller.js

@@ -23,7 +23,7 @@ export default class extends Controller {
             cache: this.element.hasAttribute('data-cache'),
             animateHistoryBrowsing: this.element.hasAttribute('data-animate-history-browsing'),
             plugins: [
-                'slide' === this.element.hasAttribute('data-theme') ? new SwupSlideTheme() : new SwupFadeTheme(),
+                'slide' === this.element.getAttribute('data-theme') ? new SwupSlideTheme() : new SwupFadeTheme(),
                 new SwupFormsPlugin(),
             ],
         };