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