Valgrind memory loss reported for call to pthread_setspecific

Good morning,

In a program that uses VTK (see https://gitlab.kitware.com/vtk/vtk) loguru is used as third party logging for VTK. When I run a program that uses VTK and loguru through valgrind, I see the following:

```
==2056936== 8 bytes in 1 blocks are definitely lost in loss record 5 of 20,285
==2056936== at 0x64E50A5: malloc (vg_replace_malloc.c:380)
==2056936== by 0x1512E80D: strdup (in /usr/lib64/libc-2.28.so)
==2056936== by 0x329F8C77: vtkloguru::set_thread_name(char const*) (loguru.cpp:923)
```

It looks like the string passed to `pthread_setspecific` to set the thread name is duplicated with STRDUP, but never freed. Currently this is on line 1033 in loguru.cpp.