Fixed condition

I have no idea how come it was wrong here...

Author: michalbundyra

src/Standards/PSR2/Sniffs/Classes/ClassDeclarationSniff.php

@@ -239,7 +239,7 @@ public function processOpen(File $phpcsFile, $stackPtr)
                 continue;
             }
 
-            if ($implementsToken === true) {
+            if ($checkingImplements === true) {
                 $numberOfInterface += 1;
             }