Fix compilation issue on Beaglebone Black

Fixing these compilation errors:

```
../src/gpiowatcher.cc: In function 'void WatchWork(uv_work_t*)':
../src/gpiowatcher.cc:117:53: error: 'read' was not declared in this scope
../src/gpiowatcher.cc:133:53: error: 'lseek' was not declared in this scope
../src/gpiowatcher.cc:156:21: error: 'close' was not declared in this scope
```