Use Map directly in MetaFilter

Change-Id: I15545e9c7cdcbb8a913cbcf0eef7f8a2281de7a8
Signed-off-by: Lars Vogel <Lars.Vogel@vogella.com>

org.eclipse.jgit.http.server/src/org/eclipse/jgit/http/server/glue/MetaFilter.java

@@ -124,7 +124,7 @@ public class MetaFilter implements Filter {
 
 			@Override
 			public boolean contains(Object o) {
-				return m.keySet().contains(o);
+				return m.containsKey(o);
 			}
 
 			@Override