minor #9714 Fix writing of the article with a lowercase letter (lex111)

This PR was submitted for the 4.0 branch but it was merged into the 3.4 branch instead (closes #9714).

Discussion
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Fix writing of the article with a lowercase letter

Commits
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215c3de Fix writing of the article with a lowercase letter

Author: javiereguiluz

frontend.rst

@@ -51,7 +51,7 @@ Optimizing
 ..........
 
 * :doc:`Versioning (and the manifest.json file) </frontend/encore/versioning>`
-* :doc:`Using A CDN </frontend/encore/cdn>`
+* :doc:`Using a CDN </frontend/encore/cdn>`
 * :doc:`Creating a "Shared" entry for re-used modules </frontend/encore/shared-entry>`
 * :doc:`/frontend/encore/url-loader`