PSR2 rulesets: improve inline documentation

Fix PSR2.Files.ClosingTag name reference.

Author: diegocardoso93

src/Standards/PSR2/ruleset.xml

@@ -23,7 +23,7 @@
     <!-- checked by PSR2.Files.EndFileNewline -->
 
     <!-- The closing ?> tag MUST be omitted from files containing only PHP. -->
-    <!-- checked by PSR2.Files.ClosingTagSniff -->
+    <!-- checked by PSR2.Files.ClosingTag -->
 
     <!-- 2.3 Lines -->