[hotfix] Add missing Override annotations to RichFoldFunction and RichReduceFunction

flink-core/src/main/java/org/apache/flink/api/common/functions/RichFoldFunction.java

@@ -35,5 +35,6 @@ public abstract class RichFoldFunction<O, T> extends AbstractRichFunction implem
 
 	private static final long serialVersionUID = 1L;
 
+	@Override
 	public abstract T fold(T accumulator, O value) throws Exception;
 }

flink-core/src/main/java/org/apache/flink/api/common/functions/RichReduceFunction.java

@@ -34,5 +34,6 @@ public abstract class RichReduceFunction<T> extends AbstractRichFunction impleme
 	
 	private static final long serialVersionUID = 1L;
 
+	@Override
 	public abstract T reduce(T value1, T value2) throws Exception;
 }