memory leak

Hi, I used valgrind to check memory leak.

there is a reminder as following:

```
==2843320== 784,505 (488 direct, 784,017 indirect) bytes in 1 blocks are definitely lost in loss record 1,050 of 1,050
==2843320== at 0x4844FF5: operator new(unsigned long) (vg_replace_malloc.c:422)
==2843320== by 0x4C12C93: drogon::HttpClient::newHttpClient(std::__cxx11::basic_string, std::allocator > const&, trantor::EventLoop*, bool, bool) (in /usr/local/lib/libhttp_util.so)
==2843320== by 0x4BBC599: BuildClient(std::__cxx11::basic_string, std::allocator > const&, trantor::EventLoop*, std::pair, std::allocator >, std::__cxx11::basic_string, std::allocator > > const&) (in /usr/local/lib/libhttp_util.so)
==2843320== by 0x4BBDD33: util::http_util::SyncClient::SyncClient(std::__cxx11::basic_string, std::allocator > const&) (in /usr/local/lib/libhttp_util.so)
```

could you help on this?