Typo in include

I just took a quick look into your lib and got stuck due to a case sensitivity error.
In file
```NimBLE-Arduino/src/NimBLEDevice.h```, line 20 has to be written as
```#include "NimBLEScan.h"```
instead of
```#include "NimbleScan.h"```
to work in case sensitive operating systems like Linux.

Thanks,
Josef
