try to correct regex for spotbugs ignore

Signed-off-by: Andy Scherzinger <info@andy-scherzinger.de>

spotbugs-filter.xml

@@ -42,7 +42,7 @@
 		</Or>
 	</Match>
 	 <Match>
-        <Class name="~com.owncloud.android.ui.preview.MarkwonGrammarLocator" />
+        <Class name="~com\.owncloud\.android\.ui\.preview\.MarkwonGrammarLocator" />
     </Match>
 
     <Bug pattern="PATH_TRAVERSAL_IN" />