minor #1275 [TwigComponent] Fix typo in documentation (TBoileau)

This PR was squashed before being merged into the 2.x branch.

Discussion
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[TwigComponent] Fix typo in documentation

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| Issues        | Fix #1274
| License       | MIT

Remove the double quote in TwigComponent documentation.

Commits
-------

91e8932 [TwigComponent] Fix typo in documentation

Author: weaverryan

src/TwigComponent/doc/index.rst

@@ -235,7 +235,7 @@ available in every component template:
 
 .. code-block:: html+twig
 
-    <div {{ attributes.defaults({ class: 'alert alert'~ type }) }}">
+    <div {{ attributes.defaults({ class: 'alert alert-'~ type }) }}>
         {{ message }}
     </div>