fix annotation in Gedmo\Loggable\Entity\LogEntry

This commit fixes the error below:

[Doctrine\Common\Annotations\AnnotationException]                                                                                                                                                                                                                                                                                                             
[Semantical Error] The class "Table" is not annotated with @Annotation. Are you sure this class can be used as annotation? If so, then you need to add @Annotation to the _class_ doc comment of "Table". If it is indeed no annotation, then you need to add @IgnoreAnnotation("Table") to the _class_ doc comment of class Gedmo\Loggable\Entity\LogEntry.