Fix for the travis build caused by my previous commit

Summary: My previous commit ('Passing table properties to compaction callback') broke the clang build. Here is the fix.

Test Plan: USE_CLANG=1 make all -j

Reviewers: igor

Reviewed By: igor

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D48489

db/listener_test.cc

@@ -157,10 +157,11 @@ struct TestPropertiesCollector : public rocksdb::TablePropertiesCollector {
                                      const rocksdb::Slice& value,
                                      rocksdb::EntryType type,
                                      rocksdb::SequenceNumber seq,
-                                     uint64_t file_size) {
+                                     uint64_t file_size) override {
     return Status::OK();
   }
-  virtual rocksdb::Status Finish(rocksdb::UserCollectedProperties* properties) {
+  virtual rocksdb::Status Finish(
+      rocksdb::UserCollectedProperties* properties) override {
     properties->insert({"0", "1"});
     return Status::OK();
   }