Fixed a versionadded directive

Author: javiereguiluz

components/translation/usage.rst

@@ -436,7 +436,7 @@ The ``$messages`` variable will have the following structure::
 Adding Notes to Translation Contents
 ------------------------------------
 
-.. versionadded: 3.4
+.. versionadded:: 3.4
     The feature to load and dump translation notes was introduced in Symfony 3.4.
 
 Sometimes translators need additional context to better decide how to translate