Fix building fault

Former-commit-id: b669efe7c632d05d46e9eafa767998909e076f25

cpp/unittest/db/mem_test.cpp

@@ -15,7 +15,7 @@
 #include <fstream>
 #include <iostream>
 #include <cmath>
-
+#include <random>
 
 using namespace zilliz::milvus;
 

cpp/unittest/db/search_test.cpp

@@ -6,7 +6,7 @@
 #include <gtest/gtest.h>
 
 #include "db/scheduler/task/SearchTask.h"
-
+#include <cmath>
 #include <vector>
 
 using namespace zilliz::milvus;
@@ -159,4 +159,4 @@ TEST(DBSearchTest, MERGE_TEST) {
         ASSERT_EQ(target.size(), src_count + target_count);
         CheckResult(src_result[0], target_result[0], target);
     }
-}
\ No newline at end of file
+}