Uppercase sentence

Co-authored-by: Juliette <663378+jrfnl@users.noreply.github.com>

WordPress/Docs/NamingConventions/ValidVariableNameStandard.xml

@@ -21,7 +21,7 @@
         </code>
     </code_comparison>
     <code_comparison>
-        <code title="Valid: words separated by underscores.">
+        <code title="Valid: Words separated by underscores.">
         <![CDATA[
 class My_Class {
     public <em>$property_name</em> = 'value';