memory leak when using repeat(void)

after running snippet below memory increase infinitely

``` cpp
#include <rxcpp/rx.hpp>
#include <iostream>

int main(int argc,char** argv)
{
    rxcpp::sources::range(1,10)
    .repeat()
    .subscribe([](auto i)
    {
        std::cout << i << std::endl;
    });
    return 0;
}

```
