DATAES-285 - fix broken tests after 4970783

Author: xhaggi

src/main/java/org/springframework/data/elasticsearch/core/MappingBuilder.java

@@ -289,7 +289,7 @@ private static void addNestedFieldMapping(XContentBuilder builder, java.lang.ref
 	private static void addMultiFieldMapping(XContentBuilder builder, java.lang.reflect.Field field,
 											 MultiField annotation, boolean nestedOrObjectField) throws IOException {
 		builder.startObject(field.getName());
-		builder.field(FIELD_TYPE, annotation.mainField().type());
+		builder.field(FIELD_TYPE, annotation.mainField().type().name().toLowerCase());
 		builder.startObject("fields");
 		//add standard field
 		//addSingleFieldMapping(builder, field, annotation.mainField(), nestedOrObjectField);